Functions Of The Digestive System Biology Essay


WebMD (2010) states the main function of the digestive system is to break down food so that the nutrients contained in the food can be absorbed by the body. The nutrients then enter the blood for transportation to the body cells; indigestible matter is excreted as faeces.

Digestion begins in the mouth with chewing, saliva is produced to help break down the food before being swallowed through the throat and oesophagus; the oesophagus extends from the pharynx to the stomach. Through the action of peristalsis food is moved along the hollow organ of the digestive tract, peristalsis is the action of contraction in waves.

In the stomach the ingested food is further rendered by the strong acidic environment, enzymes are also produced in the stomach to help the digestion process; food leaves the stomach with the consistency of liquid or paste and is then passed in to the small intestine which is made up of three segments (duodenum, jejunum and ileum) the digestion process is continued in the small intestine, again enzymes are released this time from the pancreas and bile from the liver; bile aids assimilation of fats and also eradicates waste products from the blood.

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When the nutrients have been absorbed by the small intestine the digested matter is then passed in to the large intestine (colon) waste left over from the digestion process is passed along the colon by peristalsis, as the waste matter moves along the colon it solidifies and is stored in the sigmoid colon and is then passed in to the rectum once or twice a day, and from the rectum the waste matter is expelled by the sphincter muscle through the anus.

The Cardiovascular System

The cardiovascular system:

> Heart

> Blood vessels

Marieb(2007, p.6) & Hoehn(2007, p.6) state the main function of the cardiovascular system is to transport blood through the circulatory system via blood vessels (arteries, arterioles, capillaries, venules and veins) , the blood vessels carry oxygen, carbon dioxide, nutrients and waste products; the heart is the engine of the cardiovascular system pumping blood around the body.

The heart BUPA (2002) is roughly the size of a human fist, sits in the centre of the chest and has a protective layer called the pericardium, in one average day the heart pumps about 8,000 litres of blood around the body; the heart has a right and left side and is a muscular organ.

Blood is pumped from the right side of the heart to the lungs where it is oxygenated, the oxygenated blood is then returned to the left side of the heart which pumps the blood to the rest of the body; the left side of the heart is also slightly larger than the right side due to its increased workload.

The left and right sides of the heart are both divided into upper and lower chambers, called an atrium & ventricle; blood moves from the aria to the ventricle via a muscular one way valve.

The Renal System

The renal system:

> Kidney s

> Ureter

> Urinary bladder

> Urethra

Marieb (2007, p.7) & Hoehn (2007, p.7) state the renal system eliminates nitrogenous waste products from the body; it also normalizes water, electrolyte and acid equilibrium of the blood. (2010) the kidneys are located towards the back of the abdomen and are large, bean shaped organs.

Epithelial Tissue

Marieb (2007, p.118) & Hoehn (2007, p.118) cites the epithelium as a layer of cells that covers a surface on the human body or in a body cavity. It is formed in the body as covering & lining epithelium & also as glandular epithelium, covering & lining epithelium makes up the outer layer of the skin and lines the open cavities of the cardiovascular, digestive and respitory systems.

Glandular epithelium forms the glands of the body, epithelial tissue also forms borders amongst the different environments in the body. Epithelium of the skin protects the tissues underneath from chemical and mechanical damage and from bacterium; it also contains nerve endings that respond to stimuli from the skins surface.

Epithelial tissue lining of the digestive tract is specialised to absorb substances and in the kidneys it performs nearly all functions (excretion, absorption, secretion & filtration). Epithelial have an apical surface, an upper surface that is exposed to the exterior of the body or internal organ cavity, and a basal surface.

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Epithelial cells fit closely together to form continuous sheets, except for glandular epithelial; epithelial sheets rest on and are supported by connective tissues.

Muscle Tissue

Marieb (2007, p.139-140) & Hoehn (2007, p.139-140) mention muscle tissues are responsible for most types of movement, they are cellular and well vascularised; muscle cells also possess myofilaments, myofilaments bring movement/contraction in all cell types.

Skeletal muscle is contained by connective sheets of tissue in to organs called skeletal muscles, these muscles are attached to the skeleton, they form the flesh of the body and contract to cause movement; skeletal muscle fibres are long and cylindrical.

Cardiac muscle is only found in the heart walls, the contractions of the cardiac muscle pump blood through blood vessels. Smooth muscle does not have any visible striations; smooth muscle is located mostly in the walls of the hollow organs, except for the heart. Smooth muscle squeezes substances through (digestive & urinary tract, uterus & blood vessels) by alternating contracting/relaxing.

Blood Plasma

Marieb (2007, p.648) & Hoehn (2007, p.648) indicate blood plasma has a sticky consistency & a straw like colour; it is mostly water (90%). Over 100 different solutes can be found in the plasma, some of which are:

> Nutrients

> Gases

> Hormones

> Waste products (cell activity)

> Ions

> Proteins

The most abundant constituent of blood plasma is plasma protein (8%) by weight and most are produced by the liver, plasma proteins have a wide variety of functions but are not used as fuel by cells.

Albumin makes up about 60% of plasma protein, its function is to carry certain molecules through circulation, is a blood buffer and a major blood protein that contributes to the plasma osmotic pressure; sodium ions are the other major solute contributing to osmotic pressure.

Plasma varies as cells add/remove substances to blood; plasma composition is relatively constant and kept so by numerous homeostatic mechanisms. As wells as transporting different solutes around the body, plasma also distributes heat.