Different Parts Of The Nervous System Biology Essay


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Anterior cutaneous branch of femoral nerve- cutaneous branches of the femoral nerve distributed to the anterior and medial aspects of the thigh; they convey general sensation.

Auricutemporal nerve- The auriculotemporal nerve is a branch of the mandibular nerve that runs with the superficial temporal artery and vein, and provides sensory innervation to various regions on the side of the head.

Axillary nerve-The axillary nerve is a nerve of the human body, that comes off the superior trunk, posterior division, posterior cord of the brachial plexus of the brachial plexus at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. The axillary nerve travels through the quadrangular space with the posterior circumflex humeral artery and vein.

Brain- The portion of the vertebrate central nervous system that is enclosed within the cranium, continuous with the spinal cord, and composed of gray matter and white matter. It is the primary centre for the regulation and control of bodily activities, receiving and interpreting sensory impulses, and transmitting information to the muscles and body organs. It is also the seat of consciousness, thought, memory, and emotion.

Common palmar digital nerve- Any of four nerves in the palm of the hand that send branches to the adjacent sides of two digits. Three of these nerves are branches of the median nerve; the fourth is from the ulnar nerve.

Common peroneal nerve- A terminal division of the sciatic nerve, passing through the lateral portion of the popliteal space to opposite the head of the fibula where it divides into the superficial and the deep peroneal nerves.

Cutaneous branch of intercostals nerve- The lateral abdominal cutaneous branch of intercostal nerve (or lateral cutaneous branches) are nerve branches that supply the skin of lateral part of torso. The rest of the torso is innervated by the ventral and dorsal cutaneous branches.

Deep branch of ulnar nerve- The deep branch of the ulnar nerve is a terminal, primarily motor branch of the ulnar nerve

Deep peroneal nerve- A terminal branch of the common peroneal nerve, passing into the anterior compartment of the leg and supplying the anterior tibial muscle, the long extensor muscle of the big toe, the long extensor muscle of the toes, the third peroneal muscle, the skin of the big toe, and the medial surface of the second toe.

Dorsal branch of spinal nerve- The posterior (or dorsal) branches (or divisions) of the spinal nerves are as a rule smaller than the anterior divisions. They are also referred to as the dorsal rami. They are directed backward, and, with the exceptions of those of the first cervical, the fourth and fifth sacral, and the coccygeal, divide into medial and lateral branches for the supply of the muscles and skin of the posterior part of the trunk.

Dorsal digital nerves- Nerves supplying the skin of the dorsal aspect of the proximal and middle phalanges of the toes.

Facial nerve-The facial nerve is responsible for contraction of the muscles of the face, for production of tears from a gland (lacrimal gland) located under the upper eyelid and for conveying the sense of taste from the front part of the tongue (via the chorda tympani nerve).

Femoral nerve- The femoral nerve, the largest branch of the lumbar plexus, arises from the dorsal divisions of the ventral rami of the second, third, and fourth lumbar nerves. It descends through the fibers of the Psoas major, emerging from the muscle at the lower part of its lateral border, and passes down between it and the Iliacus, behind the iliac fascia; it then runs beneath the inguinal ligament, into the thigh, and splits into an anterior and a posterior division. Under the inguinal ligament, it is separated from the femoral artery by a portion of the Psoas major.

Filum nerve- The filum terminale ("terminal thread"), is a delicate strand of fibrous tissue, about 20 cm. in length, proceeding downward from the apex of the conus medullaris

Gluteal nerve- The superior gluteal nerve is a nerve that arises from the fourth and fifth lumbar nerves and the first sacral nerve and supplies the gluteus medius and minimus muscles and tensor muscle of the broad fascia.

Lateral pectoral nerve- The lateral pectoral nerve (lateral anterior thoracic) arises from the lateral cord of the brachial plexus, and through it from the fifth, sixth, and seventh cervical nerves. The lateral pectoral nerve passes across the axillary artery and vein, pierces the coracoclavicular fascia, and is distributed to the deep surface of the Pectoralis major. It also sends a filament to join the medial anterior thoracic and form with it a loop in front of the first part of the axillary artery.

Lateral plantar nerve- The lateral plantar nerve (external plantar nerve) is a branch of the tibial nerve, in turn a branch of the sciatic nerve and supplies the skin of the fifth toe and lateral half of the fourth, as well as most of the deep muscles, its distribution being similar to that of the ulnar nerve in the hand.

Lliohypogastric nerve- The iliohypogastric nerve is the superior branch of the anterior ramus of spinal nerve L1 (one of the lumbar nerves) after this nerve receives fibers from T12 (subcostal nerve).

Llioinguinal nerve- The ilioinguinal nerve is a branch of the first lumbar nerve. It separates from the first lumbar nerve along with the larger iliohypogastric nerve.

Medial plantar nerve- One of the two terminal branches of the tibial nerve running along the medial aspect of the sole to supply the abductor muscle of the big toe and the short flexor muscle of the toes and innervating the skin of the medial part of the foot and the medial three and one-half toes.

Median nerve- The median nerve is formed by the union of the lateral and medial cords of the brachial plexus and carries fibres derived from the 6th, 7th and 8th cervical and the 1st thoracic spinal segments. It lies close to the brachial artery in the upper arm and passes under the transverse carpal ligament as it approaches the palm of the hand.

Muscular branch of femoral nerve- The muscular branches are the nerves to: iliacus, pectineus, sartorius and the 4 heads of quadriceps

Muscular branch of the median nerve- The recurrent branch of the median nerve (which has also been called "the million dollar nerve" is the branch of the median nerve which supplies the thenar muscles

Musculocutaneous nerve- The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis minor, its fibers being derived from C5, C6 and C7.

Obturator nerve- The obturator nerve arises from the ventral divisions of the second, third, and fourth lumbar nerves; the branch from the third is the largest, while that from the second is often very small.

Optic nerve- The optic nerve (also known as cranial nerve II) is a continuation of the axons of the ganglion cells in the retina.  There are approximately 1.1 million nerve cells in each optic nerve.  The optic nerve, which acts like a cable connecting the eye with the brain, actually is more like brain tissue than it is nerve tissue.

Phrenic nerve- The phrenic nerve originates mainly from the 4th cervical nerve, but also receives contributions from the 5th and 3rd cervical nerves (C3-C5) in humans. The phrenic nerves contain motor, sensory, and sympathetic nerve fibers. These nerves provide the only motor supply to the diaphragm as well as sensation to the central tendon. In the thorax, each phrenic nerve supplies the mediastinal pleura and pericardium.

Pudental nerve- The pudendal nerve is a mixed somatic and autonomicnerve in the pelvic region which is a large branch of the sacral plexus (L4-5, S1-4) that innervates the external genitalia of both sexes, as well as sphincters for the bladder and the rectum. It originates in Onuf's nucleus in the sacral region of the spinal cord.

Radial nerve-The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm, as well as the associated joints and overlying skin.

Saphenous nerve- a large branch of the femoral nerve that supplies the skin from the knee to below the ankle with sensory nerves.

Sciatic nerve- The sciatic nerve is the longest nerve in your body. It runs from the back of your pelvis, through your buttocks, and all the way down both legs, ending at your feet.

Spinal cord- The Spinal cord is the major column of nerve tissue that is connected to the brain and lies within the vertebral canal and from which the spinal nerves emerge. Thirty-one pairs of spinal nerves originate in the spinal cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

Spinal ganglion- A spinal ganglion contains the cell bodies of sensory neurons entering the spinal cord. Bundles of myelinated nerve fibers surrounded by Schwann cells (which produce myelin) run through the middle of the spinal ganglion, while at its periphery are groups of large, round cell bodies with centrally located nuclei. The cell bodies are surrounded by flattened support cells, the satellite cells, and a thin outer capsule of connective tissue. The spinal ganglion is covered by a dense connective tissue capsule.

Subcostal nerve- The ventral branch of the 12th thoracic nerve, supplying parts of the abdominal muscles and giving off cutaneous branches to the skin of the lower abdominal wall and to the gluteal region.

Superficial peroneal nerve- A branch of the common peroneal nerve that passes downward in front of the fibula to supply the long and short peroneal muscles and terminates in the skin of the dorsum of the foot and of the toes.

Supraclavicular nerve- The suprascapular nerve arises from the trunk formed by the union of the fifth and sixth cervical nerves. It innervates the supraspinatus muscles and infraspinatus muscles.

The inferior gluteal -nerve is a nerve that arises from the fifth lumbar nerve and the first and second sacral nerves and supplies the gluteus maximus muscle.

Tibial nerve- The tibial nerve is a branch of the sciatic nerve. The tibial nerve passes through the popliteal fossa to pass below the arch of soleus.

Ulnar nerve- The ulnar nerve is derived from the medial cord of the brachial plexus and carries fibres from the 8th cervical nerve and 1st thoracic nerve

Vagus nerve-One of a pair of nerves that originate in the medulla oblongata, and extend down into the thorax and abdomen to innervate the heart, lungs, and parts of the alimentary canal. The vagus nerve carries motor neurones to the muscles which facilitate swallowing, and to both afferent neurones and efferent neurones of the parasympathetic nervous system.

The central nervous system

The central nervous system comprises of the brain and the spinal cord.

Peripheral Nervous System

Sensory Nervous System - sends information to the CNS from internal organs or from external stimuli. The sensory organs send that external stimuli via touch, smell, sound and taste receptors where they are then translated by the brain.

Motor Nervous System - carries information from the CNS to organs, muscles, and glands

Somatic Nervous System - controls skeletal muscle as well as external sensory organs.

Autonomic Nervous System - controls involuntary muscles, such as smooth and cardiac muscle.

- Sympathetic - controls activities that increase energy expenditures.

- Parasympathetic - controls activities that conserve energy expenditures.

Using hand drawn diagrams describe and outline the function of each type of neuron.

Motor Neuron (Efferent)

Motor neurons originate in the brain, spinal cord and autonomic ganglia. Impulses are transmitted to the muscles and glands from there.

The two types of motor neurons are somatic and autonomic nerves:


The somatic nervous system (SNS) is the part of the peripheral nervous system associated with the voluntary control of body movements through the action of skeletal muscles, and with reception of external stimuli, which helps keep the body in touch with its surroundings (e.g., touch, hearing, and sight).The system includes all the neurons connected with skeletal muscles, skin, and sense organs. The somatic nervous system consists of efferent nerves responsible for sending brain signals for muscle contraction.


The autonomic nervous system regulates key functions of the body including the activity of the heart muscle (see below), the smooth muscles (e.g., the muscles of the intestinal tract), and the glands.

The autonomic nervous system is a part of the peripheral nervous system that functions to regulate the basic visceral (organ) processes needed for the maintenance of normal bodily functions. It operates independently of voluntary control, although certain events, such as emotional stress, fear, sexual excitement, and alterations in the sleep-wakefulness cycle, change the level of autonomic activity.

The autonomic system is usually defined as a motor system that innervates three major types of tissue: cardiac muscle, smooth muscle

, Sensory neuron (afferent)

Sensory neurons are typically classified as the neurons responsible for converting external stimuli from the environment into internal stimuli. They are activated by sensory input (vision, touch, hearing, etc.), and send projections into the central nervous system that convey sensory information to the brain or spinal cord.

When the action potentials are generated by the sensory receptors on the dendrites of these neurons. They are transmitted to the spinal cord by the sensory nerve fibres. The impulses can then pass to the brain or the connector neurons of reflex arcs in the spinal cord.


An interneuron, also known as an associated neuron, is a neuron located entirely within the central nervous system that conducts signals between neurons. The central nervous system consists of nerve cells within the brain and spinal cord, as opposed to the peripheral nervous system, which is completely composed of nerve cells outside the spinal cord and brain. An interneuron acts as a middle-man between neurons, allowing efferent neurons, afferent neurons, and other interneuron's to communicate with one another.

Neuron types

Unipolar- These have a projection that divides into one axon: they are usually sensory neurons

Bipolar- This type, which is found in the retina and inner ear, has one axon and one dendrite.

Multipolar- Most neurons in the brain and spinal cord are multipolar. They have an axon and several dendrites.

Explain the process of the nerve impulse initiation and transmission.

The initiation of an impulse is caused by the stimulation of the sensory nerve endings or by an impulse originating from another nerve.

The action potential, that is, the transmission of the impulse, is attributed to movement of ions across the nerve cell membrane.

The nerve cell in a resting state is polarised due to the differences in concentrations of ions across the plasma membrane. So on each side of the membrane there is a different electrical charge. This is called resting membrane potential. During a resting state the outside charge is positive and the inside is negative. The main ions involved are sodium (na+) and potassium (k+).

In the resting state, the ions continually have a tendency for them to diffuse along their concentration gradients. If they are stimulated the permeability of the nerve cell membrane to these ions changes.

To begin, depolarisation occurs when NA+ floods into the neuron from the ECF, this creates a nerve impulse or action potential. As this is very rapid, it enables the conduction of nerve impulse along the entire length of the neuron in a few milliseconds. It will only travel in one direction, ie away from the point of stimulation towards the area of resting potential. This is ensured because following depolarisation it takes time for repolarisation to occur.

Whilst this is happening K+ flows out of the neuron and the movement of these ions causes the membrane to return to its resting state, this is known as the refractory period when restimulation would not be possible.

As the neuron returns to its original state of resting, NA+ is expelled by sodium-potassium pump from the cell in exchange for K+.

In myelinated neurons, the myelin sheath's insulating properties prevent the ion's movement, therefore the electrical changes can only occur at the node of Ranvier, the gap in the myelin sheath. As an impulse happens at one node, depolarisation passes along the myelin sheath to the next node, giving an appearance of a flow that leaps from one node to the next. This is known as Saltatory Conduction.

Generally the speed is dependent on the neurons size and also the myelinated fibres can conduct faster than complete conduction or simple propagation.

Describe and illustrate the nerve reflex pathway.

A reflex is a sudden and rapid involuntary response to a particular stimulus and while it is controlled by the nervous system, it only needs a few cells to occur.

The simple reflex is purely automatic and is not a learned response, this can include a knee jerk when the knee cap is tapped. Here, despite knowing what will happen the body cannot prevent it from happening as it does not in fact have any control over this action. The receptors in the knee sends a signal to the spinal cord along the sensory nerve cell, here, within the spine a reflex arc switches the signals straight to the muscles of the leg through an intermediate nerve cell followed by a motor nerve cell, contracting the leg and thus a jerk of the leg. One use for this reflex is avoidance of pain, for example, removing a hand quickly when feeling something sharp. However with the pain, higher animals such as humans can involve the brain and override this response.

Reflex arcs involve the body protecting itself by removing the consideration of taking action and thus do not involve conscious thought. Impulses travel along fewer neurons and so produce a response in the shortest possible time. The slowest steps in the pathway taken by nerve impulses are at the synapses. In many reflex arcs the number of synapses to cross may be as low as three.


The sensory organs structures are intrinsically related to their function. Discuss

Each structure of the senses we have has evolved to provide maximum efficiency in helping us to interpret the world around us through touch, smell, sight, sound and taste.

We can assess for example, a dangerous situation using many of the senses and respond quickly and thus preventing harm. This can only happen because our senses have evolved to allow us to do so and the structure of the organs of these senses is designed to gain maximum amounts of information and provide a means for a reaction following the sensation.

This essay will discuss how each of the organs involved in the receipt and interpretation of the external stimulus are structured to provide this efficiency.

The sense of smell

http://www.faqs.org/health/images/uchr_04_img0433.jpg Figure

Smell or olfaction, is mediated by specialized sensory cells of the nasal cavity, known as the olfactory epithelium, which are high in the nasal cavity above the turbinate bones.

Although this sense is not as developed as some other animals, we are able to distinguish between different substances and in fact we can detect more than 10,000 odours. (Figure 1)

The olfactory system consists of receptor cells, which are bipolar neurons, sustentacular cells and basal or stem cells. Every 1-2 months new cells are generated by the stem cells as prolonged exposure to the external environment by the receptor cells can result in damage.

The supporting cells are epithelial cells which contain enzymes that oxidize hydrophobic, volatile odorants, making them less lipid-soluble and therefore less able to penetrate membranes to enter the brain.

Into the nasal cavity, each bipolar sensory neuron projects one dendrite which ends in the cilia. It also has a single unmyelinated axon which projects through holes in the cribriform plate of the ethmoid bone into the olfactory bulb of the cerebrum, here it synapses with second order neurons. (Pocock G, Richards C, 2009)

Due to the position and how each sense relates to another in terms of forming a 'complete picture', the sense which has a direct influence from smell is taste.

The sense of taste

Figure http://bioactive.mrkirkscience.com/41/images/ch41c3.gif

Taste or gustation, is the sense for perceiving and distinguishing the sweet, sour, bitter, or salty quality of a dissolved substance, mediated by taste buds on the tongue. (Figure 2)

More than 9,000 taste buds on the tongue are responsible for the chemoreception of taste. Some taste buds are also found on the roof of the mouth and throat.

Taste receptor cells or taste buds are mainly within nodules called papillae on the surface of the tongue. These receptors take the signals received and via nerve fibres from one of the three cranial nerves travel to the brain to be 'translated'. (DK, 2001) (Figure 3)

http://z.about.com/d/biology/1/0/w/1/tastebuds.gif Figure

Each taste bud is made up of taste cells, which have sensitive, microscopic hairs called microvilli.

A taste bud is a cluster of taste cells (or receptor cells), gustatory afferent axons and their synapses with taste cells and basal cells.

Microvilli at the apical end of the taste cells extend into taste pore, the site where chemicals dissolved in saliva can interact directly with taste cells.

Those tiny hairs send messages to the brain, which interprets the signals and identifies the taste for you.

The nerve impulses are sent along the nerve fibres before synapsing in the medulla and thalamus before finally ending in the parietal lobe of the cerebral cortex where taste is perceived. (Waugh A, 2006)



The eyeball is the sense organ for sight situated in the orbital cavity and is supplied by the second cranial nerve. (Figure 4)

With a diameter of approximately 2.5 cm, it is almost spherical in shape and the space between the eye and the orbital cavity is occupied by adipose tissue, this helps provide protection along with the bony walls of the cavity. (Patton K, 2007)

The eyeball has three layers known as tunics. Firstly there is the outer layer which consists of the sclera and cornea.

The sclera or white of the eye forms the outermost layer of the posterior and lateral aspects of the eyeball and is continuous anteriorly with the transparent cornea. There is a firm fibrous membrane which keeps the shape of the eye and acts as an attachment to the extrinsic muscles of the eye.

The cornea is a curved structure which bends light rays to focus them on the retina. It is a clear epithelial membrane and is convex anteriorly. It covers the pupil, iris, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. (DK, 2001)

The central tunic or uveal tract consists of the iris, ciliary body and the choroid.

The iris is the coloured part of the eye and extends anteriorly from the ciliary body, behind the cornea and in front of the iris. It is composed to pigment cells and smooth muscle fibres, one circular and one radiating. Within the centre there is an aperture called the pupil and the control of dilation is done by the parasympathetic and sympathetic nerves which constrict and dilate allowing for more or less light to enter depending on requirements. (Patton K, 2007)

The choroid lines the inner surface of the sclera, it has an excellent blood vessel supply and its main function is to absorb the light which has entered the eye through the pupil.

The ciliary body is the continuation of the choroid consisting of ciliary muscles which contract and relax allowing a change in thickness of the eye and thus bending rays of light and secretory epithelial cells which secrete aqueous fluid into the anterior of the eye.

The third layer of the eye forms the retina where the light rays converge and images are formed. This is an extremely delicate part of the eye and lines about three quarters of the eyeball, with the thickest part at the back.

Several layers of nerve cells and their axons compose the retina, where the light sensitive layer contains the rods and cones which contain photosensitive pigments which convert light rays into nerve impulses, then to be sent to the brain. (Patton K, 2007)

To support the eyeball several accessory structures provide protection and other useful functions. The eyebrows, eyelashes and eye socket, serve to protect the eye from foreign objects entering the eye. The tear duct provides lubrication to prevent the eye drying out and also protect the eye.



The ear is the organ responsible for our hearing, which also plays a vital role in balance. It is supplied by the 8th cranial nerve which is stimulated by vibrations caused by sound waves.

The ear has three parts; the external, middle and the cochlea of the internal ear which is concerned with hearing and also comprises of the semi-circular canals, the utricle and the sacule of the internal ear, which are concerned with the bodies balance. (Watson, 2005)

The external part of the ear consists of the auricle and the external acoustic meatus or auditory canal.

The auricle is the part of the ear which is projected from the side of the head and is composed of fibroelastic cartilage which is covered with skin. The lobule or ear lobe is supplied with blood and is the lower part of that region.

Leading from the auricle is the external acoustic meatus. This leads from the outer part of the ear to the ear drum via a 2.5 cm long s shaped tube to the tympanic membrane. Along this route there are a number of hair follicles and ceruminous glands which are modified sweat glands that produce ear wax, a way to protect the ear from foreign bodies. (Pocock G, 2009)

The middle ear is an air filled cavity within the petrous portion of the temporal bone. This entire area including its contents are lined with simple Squamous and Cuboidal epithelium. This air within a pressured area vibrates when sound waves hit it. Following this pressured area are the auditory ossicles (the malleus, incus and stapes) which are small bones within the ear which serve to transmit the sounds to the cochlea.

Lastly, the inner ear contains the bony labyrinth and the membranous labyrinth, where the hearing and the balance is controlled.

The bony labyrinth is the cavity which comprises of the vestibule (expanded part nearest middle ear), the cochlea (Auditory portion of the inner ear. Its core component is the Organ of Corti, the sensory organ of hearing, which is distributed along the partition separating fluid chambers in the coiled tapered tube of the cochlea.) And the semicircular canals (three tiny, fluid-filled tubes in your inner ear that helps keep balanced.) (Pocock G, 2009)

The Membranous labyrinth lies within the bony counterpart and comprises of the cochlea, the vestibule (dedicated to balance) and three semicircular canals.


Picture of Skin and ReceptorsFigure

The sense of touch works because of the sensory receptors based within the deep tissue or skin. Signals from these receptors are taken to the spinal cord and along to the brain where they are interpreted. (Figure6)

A free nerve ending is an unspecialized, afferent nerve ending which is found everywhere in the skin, they respond to pain, temperature, touch and pressure and they function as cutaneous receptors.

Merkel's nerve endings are mechanoreceptors found in the epidermis and mucosa which provide touch information to the brain. The information they provide are those regarding pressure and texture.

Sensory receptor of hair shaft responds to slight movements of the hair shaft.

Pacianian corpuscles are nerve endings in the skin, responsible for sensitivity to pain and pressure.

Ruffini's end-organ detects heat

End-bulb of Krause detects cold

Tactile Corpuscles of Meissner are grouped on the skin of the fingertips, lips, and orifices of the body and the nipples. Only stimulated when touched, meissner corpuscles tell the brain the shape and feel of an object. (DK, 2001)

Each sense organ has very different functions and appears to work independently from each other, it is on closer inspection that we can see how intrinsically they are related to the functions and indeed each other.

Our senses give us a complete picture of the world around and function so well because of how they are structure to maximise all of the information being received and quickly passed for interpretation by the brain.


DK. (2001). Human Body. London: Dorling Kindersley LTD.

Patton K, T. G. (2007). Anatomy and physiology. Missouri: Mosby Elsevier.

Pocock G, R. C. (2009). The human body- An introduction to biomedical and health sciences. Oxford: Oxford press.

Watson, R. (2005). Anatomy and physiology for nurses. London: Harcourt Publishers LTD.

Waugh A, G. A. (2006). Anatomy and physiology in health and illness. London: Churchill Livingstone.


Hand draw the major endocrine organs and explain their functions.

The endocrine organs and their functions

Hypothalamus- In this cluster of nerve cells at the base of the brain hormones are produced to stimulate other glands to produce their own hormones.

Pituary gland- Alongside the hypothalamus, it produces and secretes many hormones that travel throughout the body, directing certain processes stimulating other glands to produce different types of hormones.

Thyroid gland- A small gland just beneath the hypothalamus in the brain that secretes follicle stimulating hormone (FSH) and luteinizing hormone (LH).

Pineal gland- Secretes melatonin which may influence sexual development

Parathyroid gland- A gland that regulates calcium, located behind the thyroid gland in the neck. The parathyroid gland secretes a hormone called parathormone (or parathyrin) that is critical to calcium and phosphorus metabolism.

Heart- The heart produces a hormone called atriopeptin which reduces the blood volume and pressure

Adrenal gland- Located on each kidney, they produce a hormone that can influence the body's response to stress.

Kidney- The production of blood cell in the bone marrow is done by the secretion of erythropoietin by the kidneys.

Pancreas- The pancreas controls the hormone that regulates blood sugar levels.

Stomach- Hormones secreted by the stomach lining stimulates production of enzymes which aid digestion.

Intestines- Endocrine cells in the intestinal tissue secrete hormones which aid digestion.

Ovary- The ovaries produce the sex hormones oestrogen and progesterone.

Testis- The testis produces testosterone which control sperm production.

Explain and discuss the effects of hormones on the metabolism.

Hormones are excreted by several organs to suit different purposes to regulate our body functions and maintain good health. One of the important functions of the hormones is related to metabolic balance and control.

This essay is going to discuss and explain the effect that hormones have on our metabolism, looking at detail at the different hormones involved, the organs which excrete them and a few examples of disorders relating to them.

Metabolism is regulated at several levels. With regulatory mechanisms that operate entirely within the individual cell, the main purpose is to adjust the throughput of catabolic pathways such as to keep up a ready supply of ATP, NADPH and so on. This is done largely by feedback inhibition and forward activation by key metabolites such as ATP and acetyl-CoA. In contrast, hormonal control is about the obligations of a cell to the organism as a whole. Hormones are released as a response to the impending metabolic situation of the body. A good example is the secretion of insulin in response to high blood glucose levels, and the secretion of glucagon in response to low glucose levels. Hormones may also be secreted in anticipation of an imminent change of the metabolic situation, as is the case with the 'fight-and-flight' hormones epinephrine and norepinephrine. Other hormones with major effects on energy metabolism are the glucocorticoids (cortisone and hydrocortisone) and the thyroid hormones (tri- and tetraiodothyronine). (Patton K, 2007)

Firstly, the endocrine pancreas consists of the pancreatic islets (or islets of Langerhans) and serves as a major regulator of glucose, lipid and protein homeostasis. It produces glucagon and insulin from the α and β cells respectively.

Alpha cells form around 25% of the total number of these islets and are to produce glucagon which is produced as a response to a drop in blood sugar, raising it by stimulating the conversion of glycogen to glucose.

Beta cells then account of the remained 75% of the islets and have the purpose of producing insulin which counters a rise in blood sugar which could prove harmful should it continue to rise. (Watson, 2005)

To function, these hormones must be in perfect balance. A dysfunction in hormone production can result in a condition known as diabetes, causing varying levels of blood sugar which the body cannot effectively deal with. Left untreated, this can result in coma or even death.

The adrenal glands secrete several hormones and are located above and in front of each kidney close to the peritoneum. The glands are in fact quite separate in that they have two parts. The inner part or the medulla which produces the hormones epinephrine and norepinephrine and the outer part or the cortex which produces the mineralocorticoids, the glucocorticoids and sex hormones.

The mineralocorticoids regulate the electrolyte metabolism and the mineralocorticoids adosterone regulates the concentrations of minerals such as sodium and potassium, in turn affecting water content of the tissues. (Watson, 2005)

Glucocorticoids play a very important role in the carbohydrate metabolism. Cortisol and cortisone are the main glucocorticoids and they increase the conversion of protein to glycogen for gluconeogenesis and also help decrease the glucose in cells which in turn increases blood sugar level.

Over production of the cortical hormones can result in Cushing's disease which causes oedemas, increased plasma volume and raised ph. However the underproduction can also cause problems such as Addison's disease which causes anaemia, muscle weakness, low blood sugar, high blood pressure and bronzing of the skin and mucous membranes. (Watson, 2005)

The medulla also produces two hormones, norepinephrine and epinephrine. These assist with the flight or flight response of the body by stimulating the general metabolic activity of the cells, increases blood sugar levels, etc. It is a very rapid response due to the control of the medulla by preganglionic neurons of the sympathetic nervous system without interruption. (Patton K, 2007)

The thyroid gland is situated at the front and side of neck and consists of two lobes, one on either side, joined by a narrower portion called the isthmus. Here two hormones are produced, thyroxine and triiodothyronine.

The function of thyroxine is to regulate metabolism in the tissues, increases urine production when required, ensures correct development of the brain, increases protein breakdown and encourages the uptake of glucose by the cells. (Watson, 2005)

Triiodothyronine is very similar to thyroxine but with a much quicker effect. With both of them, undersecretion can lead to myxoedema in adults, which is course hair and skin and in children it can cause thyroid cretinism which left untreated can cause learning disabilities and small stature.

Over secretion can lead to thyrotoxicosis where there is an increase in metabolic rate leading to anxiety fast pulse, weight loss and a possibility of exophthalmos which is the protruding of the eyeballs. (Patton K, 2007)

The Pituary gland is located in the hypophyseal fossa of the sphenoid bone situated at the base of the skull. This gland contains both the anterior lobe and the posterior lobe.

The posterior lobe secretes two hormones. Firstly, the ADH or antidiuretic hormone causes the kidneys to increase their reabsorbtion of water, for less urine to be produced. The hormone can also produce a small amount of vasoconstriction, although mainly in the coronary vessels. (Thibodeau, 1992)

Undersecretion of this hormone can lead to diabetes insipudus, which results from less water being reabsorbed and the urine being much diluted.

The other hormone produced by the posterior lobe is oxytocin which promotes general contraction of the unstriped muscle of the body, however its main function is to affect the pregnant uterus and area around the ducts of the breasts.

The anterior lobe, also known as the master gland, produces many more hormones including thyroid stimulating hormone, somatotropin, follicle stimulating hormone, adrenocorticotrophic hormone, prolactin and luteinizing hormone. (Mackean, 1988)

Thyroid stimulating hormone or TSH, is a huge influence on all of the thyroids gland function including manufacture of hormones, stimulation of the accumulation of iodine for production of hormones, the regulation of the metabolic rate, the breakdown of fat and within certain tissues, an increase in water content.

The next hormone is adrenocorticotrophic hormone which regulates secretion, maintenance and development of the cortex. Its also involved in the bodies response to stress although not as much as its involvement in the mobilization of fats, leading to hypoglycaemia and glycogen.

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