Differences In Human And Amphibian Skin Biology Essay


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1.Sketch and label a cross-section through human skin. Identify three structural differences that would occur if this were the skin of an amphibian, rather than a human.

In humans, we have hair on our epidermis that produces insulation but amphibians lack hair and instead, have smooth, moist skin that allows them to breathe underwater. While human skin has sweat pores that secrete sweat and other waste, amphibians have gills that allow for gas exchange. The blood vessels in our dermis provide nourishment and remove wastes. Amphibians use their network of capillaries to take in oxygen.

2.Compare and contrast REM and non-REM sleep.

Sleep is a state where consciousness is reduced, sensory activity suspended, and voluntary muscles inactivated. There are two stages of sleep, REM and non-REM sleep. REM stands for Rapid Eye Movement. When we sleep, we are sleeping about 20% of REM sleep. During REM sleep, we are deeply asleep and have vivid dreams. Breathing becomes irregular and more rapid. REM sleep is often referred to as “active brain, inactive body.” While the body is limp and paralyzed, the brain is active as it recalls some of our most vivid dreams. In non-REM sleep, often known as drowsy or dreamless sleep, we are not deeply asleep instead we have brief, fragmented dreams that are often forgotten. During non-REM sleep, our breathing and heartbeat are slow and regular.

3.Compare the structure and function of three of the following types of blood vessels: arteries, arterioles, veins, and capillaries.

Blood vessels




Wall three times as thick as veins; outer layer of connective tissue containing elastic fibers allow the vessels to stretch and recoil; middle layer containing smooth muscle and elastic fibers

Carries blood away from heart to organs in body; elastic recoil maintain blood pressure; control blood flow


Muscular walls; extends and branches out from artery leading to capillaries

conveys blood between artery and capillary bed


Same two layers of tissue surrounding endothelium as arteries

Carries blood to heart; valves maintain unidirectional flow of blood


Smallest blood vessel, very thin walls,

Facilitates exchange of substances between the blood in capillaries and the interstitial fluid

4.Briefly explain why allergies, such as hay fever, are characterized as a hypersensitive immune response.

 Allergies, such as hay fever, are characterized as a hypersensitive immune response because undesirable responses to certain antigens called allergens are produced by the immune system. Allergies such as hay fever release histamines that trigger inflammatory responses such as sneezing, runny nose, tearing eyes, and smooth muscle contractions that lead to difficulty in breathing. When an individual inhales in pollen or dust, the allergen triggers antibodies called IgE. These antibodies bind to mast cells which release histamines and other inflammatory agents from granules (vesicles), in a process called degranulation.

5.Identify a respiratory pigment, then describe its structure and how this relates to its function.

 An example of a respiratory pigment is hemoglobin in humans. Hemoglobin is an iron-containing protein that reversibly binds to oxygen in red blood cells. It has a quaternary structure, four polypeptide chains with an iron atom at the center of each chain that binds to a molecule of O2. That means one hemoglobin molecule can carry four molecules of oxygen. Its structure relates to its function. Its ability to carry four oxygen molecules allows hemoglobin to increase the oxygen-carrying capacity in the blood. The conformation of hemoglobin changes as its affinity for oxygen becomes lesser or greater. When hemoglobin's affinity is greater, the protein binds to oxygen near the lungs and transports to areas that in need of oxygen.

6.Identify and briefly explain two adaptations of diving marine mammals, such as seals and dolphins.

 Two adaptations of diving marine mammals, such as seals and dolphins, include storing large amounts of oxygen to prolong the time they could stay in the water and their ability to conserve oxygen. Diving mammals have a high concentration of oxygen-storing protein called myoglobin in their muscles which enable them to store about 25% of oxygen in their muscle. Marine mammals have slower heart rates when they dive, which aid in the conservation of oxygen. In addition to the decrease in heart rate and oxygen consumption, diving mammals swim with little muscular effort and glide passively. All of these are adaptations of diving marine mammals that allows them to stay underwater for a prolong period of time.

7.Compare and contrast the digestive process in animals with two-way flow through their digestive system and those that have a digestive system with one-way flow.

 Animals with a one-way flow through their digestive system, also known as an incomplete digestive system, only have one opening which is the mouth. These animals, such as a jellyfish, take in food through the mouth and digest the food, absorbing the food just like animals with a two-way flow digestive system. But the undigested material does not leave through a second opening; instead it is pushed back out through the mouth. This one-way digestive system is more efficient because it uses less energy. However, it limits the amount of food the animal can take in because it has to wait until the food is digested and the waste excreted before it can eat more food.

 Animals with a two-way flow through their digestive system, also known as a complete digestive system, have two openings, the mouth and the anus. These animals, such as humans and roundworms, take in food through the mouth, digest the food and absorb minerals and vitamins as the food passes through various organs of the digestive system. The undigested material then passes through the anus and out of the body. An advantage of this two-way digestive system is that we can continue eating without having to finish digesting and absorbing the food beforehand.

8.Compare and contrast the mechanism of action of a steroid and a protein-type hormone at the cellular level.

 The location in which hormone receptors can be found is important in identifying which type of hormone it is. Lipid-soluble hormones such as steroids are found in target cells while water-soluble hormones such as insulin (a polypeptide) are located on the surface of the cell. Protein-type hormones are secreted by exocytosis, travel freely in the bloodstream and bind to signal receptors located on the surface of the cell, which initiates changes in the cytoplasm or in gene transcription. Steroids, on the other hand, once secreted by secretory cells are attached to transport proteins before traveling in the bloodstream. They move across the cell membrane in the process called diffusion and bind to intracellular signal receptors located in the cytoplasm or nucleus. The combination results in a transcription factor that activates gene expression and often alters gene transcription.

 The mechanism of action of a protein-type hormone, such as epinephrine, at the cellular level triggers signal transduction. Epinephrine binds to G-protein receptors located on the surface of liver cells. This binding triggers a series of steps where cAMP acts a second messenger and activates protein kinase A. This activates enzymes that will inhibit the synthesis of glycogen and promote the breakdown of glycogen. The cellular response is glucose being released into the bloodstream by the liver.

 The mechanism of action of a steroid, such as estradiol, at the cellular level regulates gene expression. After the steroid hormone binds to the receptor, the hormone-receptor complex travels to the nucleus. There, it interacts with DNA and makes changes so the transcription of specific genes can take place.

9. Use a specific example to explain how a negative feedback mechanism may be used to regulate the function of endocrine glands.

 Negative feedback mechanisms are used to regulate the function of various endocrine glands. One example is how the pancreas and liver work together to produce insulin or glucagon in order to regulate the amount of blood glucose in the body and maintains glucose homeostasis. When the body has a high level of blood glucose (stimulated by a carbohydrate-rich meal), pancreas cells release insulin into the blood which stimulates cells to take up more glucose or the liver to convert the glucose into glycogen and store it. This causes the blood glucose level to decline. When there is a low level of blood glucose in the body (lacking a carbohydrate meal), pancreas cells release glucagon into the blood which stimulates the liver to break down glycogen and release glucose into the blood. This causes the blood glucose level to rise.

10. Briefly discuss the complementary functional roles of insulin and glucagon.

 The complementary functional roles of insulin and glucagon work to maintain glucose homeostasis in the body. When blood glucose levels increase, insulin is produced by the pancreas to decrease blood glucose levels. When blood glucose levels decrease, glucagon is produced by the pancreas which increases blood glucose levels in the body.


11. Why is saltatory conduction faster than continuous conduction?

 In a continuous conduction, action potentials travel down the axon as Na+ gates open further down the neuron. Some neurons have axons that are surrounded by a layer of electrical insulation called myelin sheath, which consists of a series of Schwann cells. These cells act as insulators and are separated by gaps of unsheathed axon called nodes of Ranvier. During saltatory conduction, the action potential jumps from node to node down the axon because the nodes are the only parts of the axon that are in contact with the extracellular fluid and are the only place where ion activity occurs, and therefore action potentials jump from node to node. Saltatory conduction is faster than continuous conduction because the nerve impulse travels faster down the neuron. In a train station, saltatory conduction can be seen as the express train that skips stops while continuous conduction can be seen as the local train that stops at every train station.

12. Although the effects of an EPSP are subliminal, explain how EPSPs affect membrane potential.

The postsynaptic membrane can have two outcomes. It can either be excited or inhibited. When Na+ gates open, the membrane becomes partially depolarized as Na+ rush into the cell, making the inside of the cell more positive. The summation of EPSPs can cause the membrane potential to reach threshold. If the threshold potential is exceeded, an action potential is produced.

13. Trace the path of a sound wave beginning from its entry into the ear to its transmission to the brain.

 When sound waves reach the outer ear, the tympanic membrane vibrates. The three bones located in the middle ear, malleus, incus, and stapes transfer these vibrations to the oval window which causes the waves in the fluid inside the cochlea to move. These pressure waves cause the basilar membrane and hair cells to vibrate. The hair cells are deflected by the tectorial membrane where the bending of the hairs one direction either increases or decreases neurotransmitter release. The frequency of action potentials is sent to the brain by cochlea nerves.

14. Trace the flow of blood entirely through both the pulmonary and systemic circulations.

 Blood is pumped from the right ventricle which goes through the pulmonary arteries to the lungs. The blood flows through capillary beds in the lungs, picking up O2 and releasing CO2. The oxygenated blood goes through the pulmonary veins to the left atrium. The blood continues to flow the left ventricle where it leaves the heart through the aorta. Via arteries, the blood is sent throughout the body and enters capillary beds found in the neck, head, arms, stomach, and legs, releasing O2 and picking up CO2. The capillaries form venules that bring the blood back to the veins. The blood travels through large veins, the superior vena cava, the inferior vena cava, and the posterior vena cava and back to the right atrium. Blood is pumped into the right ventricle and the cycle begins again.

 15. What is the significance of the circle of Willis?

 The circle of Willis is a circle of arteries that carries blood to the brain. The significance of this circle is to ensure that blood is delivered to the brain. When one artery is blocked, the circle of Willis allows the other vessels to carry the blood to the brain to prevent a shortage of blood supply in the brain, which can result in fatal consequences.

 16. Explain what occurs during the inflammatory response and how it is a protective mechanism.

 During the inflammatory response, histamine is secreted by white blood cells found in connective tissue called basophils. Stimulated by histamine, vasodilation, the dilation of blood vessels, increases blood supply to the injured part of the body. An increase in blood flow brings phagocytes to the damaged area where they destroy pathogens and engulf damaged cells. This causes redness, swelling, and a raise in temperature. The increase in temperature, like a fever, is caused by interleukin-1 released by cells in the body and stimulated white blood cells that help to fight the infection.

 17. Trace the path of a chef's salad with croutons down the digestive tract, and explain what takes place in each specialized region.

As the chef's salad with croutons enter the mouth, amylase, secreted by salivary glands in the mouth, breakdown starch (croutons) into disaccharide maltose. In addition to enzymes operating on the food, chewing reduces the size of the food particle and shapes it into a ball or bolus which is then swallowed. As the food travels down the throat or pharynx, the epiglottis blocks the trachea so that the food only enters the esophagus. The food moves down the esophagus to the stomach in a process called peristalsis (muscle contractions).

 In the stomach, gastric juice, a mixture of digestive enzymes and HCl is secreted that breakdown the food into smaller pieces. The enzyme pepsin produced by the stomach breakdown proteins (chicken). After the mixing of the food with water and gastric juice, the result is a creamy matter called chyme which enters the small intestine. In the duodenum of the small intestine, starch and protein are digested by enzymes. The villi and microvillie of the small intestine absorb the breakdown products of the food. The remaining food enters the large intestine or colon where water is reabsorbed forming feces. The solid waste is stored in the rectum and excreted through the anus.

18. Outline what is currently known about the regulation of food intake and energy homeostasis. Include the roles of leptin, neuropeptide Y, and MHC in your response.

Leptin is produced by adipose (fat) tissue. The reduction of body fat causes a decrease in leptin which causes the body to take in food. This in turn increases body fat which results in an increase in leptin, causing leptin to suppress appetite. Neuropeptide Y is produced in the hypothalamus. When leptin levels are low, nueropeptide Y increases food intake and slows down metabolism.

19. What is meant by the counterflow of fluid through the limbs of the loop of Henle and what is its role in the normal function of a human kidney?

 The counterflow of fluid through the limbs of the loop of Henle refers to the direction of filtrate passing the limps of the loop. There are two limps, a descending limb and an ascending limb. Filtrate travels down the descending limb as filtrate is moving up through the ascending limb. In the descending limb, the filtrate becomes more concentrated as water is lost out of the tube. In the ascending limb, the filtrate becomes more dilute as it loses the salt out of the tube. This prevents dehydration or excessive water loss.

 20. Explain how hormone secretion regulates the menstrual phase of the menstrual cycle.

The menstrual phase composes the first five days of the menstrual cycle. The hormones secreted by the anterior regulate the menstrual phase of the menstrual cycle. The cycle begins with the hypothalamus that releases GnRH, which stimulates the anterior pituitary to secrete hormones, follicle-stimulating hormone, FSH and luteinizing hormone, LH. FSH stimulates follicle growth. The growing follicles produce estradiol which aids in the maturing of the oocytes.

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