Hormones: Maintaining Blood Homeostasis (AQA GCSE Biology)

The endocrine system is composed of glands that secrete hormones directly into the bloodstream.

Hormones are carried around the body in the blood.

Compared to the nervous system, the effects of hormones are slower but they act for longer.

The endocrine system is composed of glands that secrete hormones directly into the bloodstream, when they reach a target cell/organ, they produce an effect.

The endocrine glands labelled X, Y and Z are:

• X = thyroid gland

• Y = pancreas

• Z = testes

The pituitary gland is a 'master gland' that secretes several hormones (such as FSH and LH) into the blood in response to body conditions. These hormones act on other glands to stimulate the release of additional hormones.

False.

Compared to the nervous system, the effects of hormones are slower but they act for longer.

A hormone is a chemical messenger molecule released from glands and transported in the blood. Hormones bring about changes in specific target cells.

The pancreas is the gland that produces and secretes insulin.

False.

Insulin reduces blood glucose levels by increasing the uptake of glucose from the blood into the body cells, where it is converted into glycogen.

When blood glucose concentration is too high, the pancreas produces the hormone insulin to bring it back down.

In liver and muscle cells, excess glucose is converted into glycogen (a polymer of glucose) for storage.

Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin to control blood glucose levels.

Type 2 diabetes is a disorder where the body cells no longer respond to insulin produced by the pancreas.

A carbohydrate-controlled diet and an exercise regime are common treatments for Type 2 diabetes.

Obesity is a major risk factor for Type 2 diabetes.

The hormone glucagon is produced when the blood glucose concentration is too low. It causes glycogen to be converted into glucose and released into the blood.

If body cells lose or gain too much water by osmosis, they do not function efficiently: too much water can cause cell lysis (bursting), and too little water can lead to cell death.

The two sources of water in the body are water produced as a result of aerobic respiration and water in the diet.

Water is lost from the body in the following ways:

• Via the lungs during exhalation

• Through the skin in sweat

• Controlled loss via the kidneys when they filter the blood to produce urine

Deamination is the process of breaking down excess proteins in the liver, where enzymes split up amino acid molecules, converting the nitrogen-containing part into ammonia, which is then converted to urea for safe excretion.

The kidneys help to control the water content of the body and the concentrations of substances (such as sodium and potassium ions) dissolved in the body fluids.

Filtration is the process where high-pressure mass flow forces small molecules like glucose, urea, and water with ions out of the bloodstream into the kidneys, forming filtrate.

During selective reabsorption, substances needed by the body are reabsorbed back into the bloodstream from the filtrate in the kidneys, including all glucose and some ions.

Urine is formed from substances not reabsorbed from the filtrate, including urea, water, and excess ions.

ADH affects the permeability of the kidney tubules to water:

• More ADH makes the tubules more permeable, leading to more water reabsorption when blood water content is low (urine is concentrated)

• Less ADH makes the tubules less permeable when the blood water content is high (urine is dilute)

Kidney failure is a condition where the kidneys do not function properly, leading to a build-up of toxic wastes in the body, which can be fatal if not treated.

Dialysis is a treatment for kidney failure where a machine acts as an artificial kidney, removing most of the urea and maintaining the water and salt balance in the blood.

A kidney transplant is a surgical procedure where a healthy kidney from a donor is implanted into a patient with kidney failure, offering a long-term solution compared to dialysis.

A kidney transplant provides:

• more freedom to the patient

• a less restrictive diet

• lower cost option (instead of dialysis machines)

• long-term solution (whereas dialysis only works for a limited time)

Disadvantages include the risk of rejection, the need for lifelong immunosuppressant drugs with side effects, and a shortage of donors.

False.

The kidneys also play a role in controlling the water content and ion concentrations in the body, as well as reabsorbing necessary substances back into the bloodstream.