Week 2: Introduction to organs

Today we ran quickly through as many organs as we could to get an idea of where they are (particularly in relation to other organs) and what they do.
The oesophagus is a muscular tube transporting fluid and food to the stomach. The stomach is a muscular bag that churns up the food and mixes it with more enzymes (after saliva) and acid, which activates another enzyme. The mixed up contents are then squirted into the duodenum – the first part of the small intestine. The small intestine (small bowel) is a 6m long coiled tube where about 90% of the absorption of nutrients into the blood occurs. It has a huge surface area, both because of its folded length and its villous surface. The large intestine (large bowel) receives the leftovers into the caecum, and the colon frames the small intestine by running up, across, and down the other side of the abdomen. It ends as the rectum. The large intestine absorbs water, electrolytes and some vitamins from its contents, and forms and stores the faeces. We noted the vermiform appendix, a length of lymphoid tissue extending from the posterior surface of the caecum.
Almost all of the blood from the gastrointestinal (GI) tract passes to the liver, rich in the nutrients from the last meal. The liver is the largest internal organ and has hundreds of functions that could be grouped into “metabolic regulation”, “haematological regulation” and “bile synthesis”. It stores carbohydrates, lipids, amino acids, and fat-soluble vitamins, removing them from or adding them back to the circulation as required, and is involved in the removal of toxins and metabolic waste (aiding the kidneys). It recycles red blood cells, makes plasma proteins, and makes bile that is added to the duodenum to emulsify fats. (A little more here).
The pancreas also adds exocrine secretions to the duodenum. Its pancreatic juice buffers the chyme (duodenal contents) and breaks down the food to component nutrients. Its endocrine secretions are insulin (signals liver cells to take glucose from the blood and store it as glycogen), glucagon (does the opposite of insulin), somatostatin (decreases glucagon and insulin secretion and slows the activity of the GI tract) and pancreatic polypeptide (decreases gallbladder contractions and exocrine pancreatic secretions).
The spleen is a lateral lymphoid organ involved in preparing the body for an immune response and, like the liver, cleans up old or damaged blood cells and other blood components. Because of its superficial location, good bloody supply and weak connective tissue capsule it is at risk of rupturing and causing internal bleeding into the abdomen with trauma.
The thymus gland is a small gland posterior to the sternum that seems to be important in the development of the immune system. It is larger in children.
Almost all of you were familiar with the structures and functions of the heart and lungs, and the differences between the left and right sides of the heart.
We looked at the kidneys, and talked about their function. While many students were aware of their roles of blood filtration, excretion of metabolic waste and regulation of water/blood volume, few made the links to regulation of blood pressure, plasma ion concentration, and pH. The kidneys also have endocrine functions (secreting hormones). More here.
Moving into endocrine glands, we looked at the location of the thyroid gland in the neck and the 4, small parathyroid glands on its posterior surface. Some hormones of the thyroid gland increase the rate of cellular metabolism and respiration, and another (calcitonin) decreases the concentration of calcium ions (Ca2+) in the blood. Parathyroid hormone, in contrast, increases the concentration of calcium ions. Calcium is one of the mineral ions that are vital to cellular function. Calcium is stored in bone and the hormones signal bone cells to store or retrieve calcium.
The adrenal glands sitting atop the kidneys make adrenaline which you’ve all hopefully met in fearful or exciting situations that maybe required a “fight or flight response”. They also make noradrenaline and adrenocorticosteroids that are vital to life, with roles (again) in metabolism.
We skipped the gonads as we didn’t have enough time, but we did talk about the pituitary gland. This pea-sized organ inside the cranium, along with the hypothalamus and other parts of the brain is a controlling centre for many of the other organs that we talked about. It is another endocrine organ, and affects the functions of the kidneys, the thyroid gland, the gonads and other reproductive organs, and it produces growth hormone (more about the hormones and some disorders here).
The session was a very rapid overview of many organs and we’ll meet them all in detail over the next year or two; some in anatomy, some in other lectures.