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Homeostasis

What are hormones?

Hormones are a chemical substance, produced by a gland, carried by blood, which alternates the activity of one or more specific target organ and is then destroyed by the liver.

Negative Feed back: Negative feed back is a feedback that tends to stabilize a process by reducing its rate or output when its effects are too great.

Endocrine glands

Endocrine glands are ductless glands which produce and release hormone directly into blood.

For example: Islets of Langerhans in pancreas and adrenal glands on the kidneys.

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  • Hormone molecules must be small, soluble and diffuse easily, so they can pass quickly from the cells that make them, into blood capillaries.

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Regulation of blood glucose concentration

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  • High concentration of glucose in blood

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When glucose concentration in blood is higher than normal, pancreas detects the high concentration of glucose and stimulates beta cells of islets of Langerhans to secrete insulin.

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  1. Insulin is transported to the liver by blood where it causes the liver to convert the excess glucose to glycogen and store it into the liver and muscles.

  2. Insulin increases the permeability of cell membrane towards glucose so that more glucose can enter the cells from blood stream.

  3. Insulin increases the rate of respiration within the cells so more glucose is used up.

  4. As a result, the glucose concentration in blood is decreased to normal.

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  • Low concentration of glucose in blood

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When there is a decreased concentration of glucose in blood, the pancreas detects it and stimulates alpha cells of Islets of Langerhans to secrete glucagon.

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  1. Glucagon is transported to the liver by blood where it causes the liver to break down glycogen to glucose.

  2. Glucagon decreases the permeability of cell membrane towards glucose, so glucose can’t enter the cells.

  3. Glucagon decreases the rate of respiration, so less glucose is used up.

  4. Glucagon stimulates gluconeogenesis, which is the formation of glucose from fat or amino acids.

  5. As a result, the blood glucose level is increased back to normal.

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Regulation of blood concentration

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  • When blood is concentrated (low water potential)

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  1. When body loses too much water e.g. by sweating, the water potential of the body decreases as a result osmotic pressure in plasma is increased.

  2. This stimulates the hypothalamus of brain which causes pituitary gland to secrete the hormone ADH into blood stream.

  3. The ADH travels through the blood and binds to the kidney tubules and make them more permeable to water so more water is reabsorbed back into blood.

  4. Less urine, concentrated urine is produced.

  5. As a result water potential in the body increases and osmotic pressure in plasma decreases to normal.

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  • When blood is dilute (high water potential)

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  1. When blood becomes more dilute, water potential of the body increases and osmotic pressure of plasma decreases.

  2. This stimulated the hypothalamus of the brain which causes the pituitary gland to not secrete ADH.

  3. So the kidney tubules remain impermeable too water, and no water is reabsorbed back into blood.

  4. More volume of dilute urine is produced.

  5. As a result the water potential of the body decreases and osmatic pressure in the plasma increases.

Human skin

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The skin is a waterproof structure, one of the organs of sense and touch.

The skin can be primarily divided into 3 segments:

  • ​Epidermis​​

    • Contains keratin, and effective waterproof layer.

    • Protects body from microbial infection, mechanical and thermal damage.

    • Replaces dead cells by mitosis.

    • Contains melanin to protect genetic material from UV radiation.​

  • Dermis​​​​

    • The inner layer of the two main layers of the skin. The dermis has connective tissue, blood vessels, oil and sweat glands, nerves, hair follicles, and other structures. It is made up of a thin upper layer called the papillary dermis, and a thick lower layer called the reticular dermis.​

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Functions of the skin:

  • Protect the body (epidermis)

    • To provide mechanical protection

    • To prevent bacterial entry

    • To reduce water loss

  • Temperature regulation (hair)

  • Provide mechanical protection

  • Prevent bacterial entry

  • Reduce water loss

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Regulation of temperature

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  • When body is exercising vigorously (or when surrounding is hot or core body temperature increases).

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  1. Thermoreceptors in skin detect and increase in environmental temperature of the blood.

  2. Sweat glands increase production of sweat so that more heat can be evaporated.

  3. Vasodilation occurs, so that more blood carrying more heat is transported towards the surface of the skin and more heat is lost by radiation.

  4. Rate of metabolic reaction within the body is decreased generating less heat.

  5. Hair erector muscles relax; hair follicles lie down trapping ho air between them so move heat can be lost as ho air that can act as insulator.

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  • When body is at rest (or when surrounding is cold or when core body temperature decreases).

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  1. Thermo-receptors in the skin detect the decrease in environmental temperature or heat sensors in the hypothalamus detect drop in temperature of blood.

  2. Sweating stops to prevent heat lost by evaporation.

  3. Vasoconstriction occurs, so less blood carrying less heat is transported to the surface of the skin, so less heat is lost by radiation.

  4. Rate of metabolic reactions increase generating more heat.

  5. Hair erector muscles contract, hair follicles stand up, trapping air between them. Less heat is lost as air acts an insulator.

  6. Shivering occurs which is the involuntary contraction and relaxation of skeletal muscles to generate heat

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Diabetes and Hormones

Type 1 diabetes

Type 1 diabetes occurs when the pancreas produces too little of the hormone insulin and in some cases no insulin at all as the insulin producing cells within the pancreas is detected as foreign cell and immune system of the body starts to destroy them. This causes blood glucose to rise to potentially lethal level.

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There are 2 main symptoms for type 1 diabetes:

  1. Higher concentration of glucose in blood

  2. Presence of glucose in urine

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Other symptoms:

  • Dry mouth

  • Blurred vision

  • Feeling Thirsty

  • Increases heart rate and breathing rate

  • Rapid weight loss

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Treatment for diabetes mellitus:

  1. Avoid too much sugary foods and carbohydrates in the diet, sugar in particular will cause a rapid rise in glucose levels which is difficult to remove without the presence of sufficient insulin.

  2. Injecting insulin which will make the liver remove excess glucose from the digested food. Insulin can greatly help diabetes in providing the necessary insulin but can never be as successful as a properly functioning normal pancreas and diabetics suffer long term heath problems.

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Role of insulin in diabetes mellitus:

Insulin can greatly help diabetes in providing the necessary insulin but can never be as successful as a properly functioning normal pancreas and diabetics suffer long term heath problems.

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  1. ​When the pancreas fails to produce enough insulin, blood glucose level rises, as a result blood glucose level rises above the normal, the kidneys excrete glucose and glucose appears in the urine. This condition is called diabetes mellitus.

  2. Glucose reserves of the body are rapidly depleted in diabetic patients, Proteins are then utilized. The oxidation of fats to provide energy results in accumulation of toxic substances which could cause the patient to fall into a diabetic coma.

  3. If insulin production is hot severely reduced, it may be possible to treat the condition by restricting the person’s intake of carbohydrates and by doing regular exercise.

  4. In most severe cases the treatment will include regular injection of insulin The carbohydrate intake must then be regulated to the match the amount of insulin injected.

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Adrenaline (hormone)

Role of the hormone adrenaline in boosting blood glucose levels and examples in which it may occur:

  • Hormone adrenaline is produced by the adrenal gland. Adrenaline mobilizes the entire body for unusual exertion due to stress, anxiety, or fear. The varies of short-term responses prepares the body for a fight or flight. The body responds to adrenaline by:

    • Stimulating liver to convert glycogen to glucose so that more glucose is available for muscle contraction.

    • Increasing the rate of heart beat so that oxygen and glucose takes less time to reach the muscles.

    • Increasing the rate and depth of ventilation, which increase the rate of uptake of oxygen by lungs.

    • Diverting blood from less important organs such as get, skin etc to the muscles.

    • Dilating pupil to enhance vision

    • Increasing blood supply to skeletal muscles.

    • Increasing metabolic rates so that more energy is available, increasing oxygen supply to body.

    • Increasing glucose supply to heart and muscles.

    • Increasing rate of blood clotting when skin is cut to prevent excessive loss of blood.

    • Constricting arterioles in skin, causing more blood to the muscles.

    • Contracting hair erector muscles to produce goose bumps and cause hair to stand on end

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