Homeostasis in humans- part 1 Higher Biology Homeostasis in humans- part 1

Human Homeostasis By the end of this lesson you should be able to: Know the principle of negative feedback Know how the water concentration of the blood is maintained. Explain the role of ADH in osmoregulation Know how the blood sugar concentration is maintained. Explain the role of insulin, glucagon and adrenaline in controlling blood sugar levels.

Physiological Homeostasis Physiological homeostasis- body’s ability to maintain relatively stable internal conditions even though the outside world changes continuously. dynamic vs. steady state is constant (example- water bath temperature control)

Physiological Homeostasis What do we mean by internal environment? The millions of cells that make up our body and the tissue fluid that bathes them is the internal environment.

Physiological Homeostasis We will look at how the body regulates: Water concentration of the blood Blood glucose levels Internal body temperature.

Physiological Homeostasis Why do we need to regulate Water concentration of the blood? Otherwise many physiological and biochemical functions would be impaired. e.g. nervous co-ordination and membrane permeability.

Physiological Homeostasis Why do we need to regulate: Blood glucose levels? To provide the energy needed by cells to perform energy demanding jobs. e.g. synthesis of protein, active transport, muscle contraction.

Physiological Homeostasis Why do we need to regulate: Internal body temperature? To provide the optimum conditions for enzyme-catalysed reactions to be carried out.

Water Bath Temperature set on thermostat Too cool? Heater kicks on and temperature goes up Too warm? Heater stays off until bath cools down Constant checking and turning on and off

Control of homeostasis through feedback Feedback system- cycle of events in which the status of a body condition is continually monitored, evaluated, changed, re-monitored, re-evaluated, etc.

3 basic components of a feedback system 1) receptor sensor that responds to changes (stimuli) 2) control centre sets range of values, evaluates input and sends output 3) effector receives output from control centre and produces a response

Osmoregulation This is where the body maintains its concentration of water, salts and ions at the correct level. The receptors are in the hypothalamus- called osmoreceptors.

Osmoregulation The control centre is the pituitary gland. It responds by producing ADH (Anti-Diuretic Hormone).

Osmoregulation ADH travels in the blood to the kidney. The effector is the tubules in the kidney. They responds by changing their permeability to water.

Osmoregulation-increase in water concentration of the blood. The water concentration of the blood can increase due to: Drinking lots of dilute liquids.

Osmoregulation-increase in water concentration of the blood. Detected by osmoreceptors in the hypothalamus. Causes pituitary gland to release less ADH. ADH travels in blood. Kidney tubules become less permeable to water. Less water reabsorbed by osmosis into the blood. Large volume of dilute urine produced. Water concentration of the blood falls back to normal.

Osmoregulation-decrease in water concentration of the blood. The water concentration of the blood can decrease due to: Sweating. Eating salty food Lack of drinking water

Osmoregulation-decrease in water concentration of the blood. Detected by osmoreceptors in the hypothalamus. Causes pituitary gland to release more ADH. ADH travels in blood. Kidney tubules become more permeable to water. More water reabsorbed by osmosis into the blood. Small volume of concentrated urine produced. Water concentration of the blood rises back to normal.

Osmoregulation Insert and complete the “Control of Blood Water Concentration” diagram

Control of Blood sugar All cells need a continuous supply of energy- glucose is therefore constantly being used up by cells. Glucose is only supplied to the body during eating. Stored glucose can be broken down as required to meet the cells demands.

Stored glucose Glucose is stored as glycogen in the liver. Two hormones are involved: INSULIN Activates the enzyme for this reaction: Glucose glycogen

Stored glucose Two hormones are involved: GLUCAGON Activates the enzyme for this reaction: Glycogen glucose

Control of Blood Glucose Levels The receptors are in the Islets of Langerhans in the pancreas. They produce insulin or glucagon

Control of Blood Glucose Levels The target organ for these hormones is the liver.

Increase in glucose concentration of the blood. The blood glucose levels (BGL) can increase due to: Eating a meal

Increase in BGL Detected by receptors in the Islets of Langerhans. These receptors cells produce insulin. Insulin travels in the blood to the liver At the liver an enzyme stores excess glucose as glycogen. BGL falls back to normal.

Decrease in glucose concentration of the blood. The blood glucose levels (BGL) can decrease due to: Between meals During the night

Decrease in BGL Detected by receptors in the Islets of Langerhans. These receptors cells produce glucagon. Glucagon travels in the blood to the liver At the liver an enzyme stores breaks down glycogen to glucose. BGL increases back to normal.

What about Adrenaline?

Practice Questions Torrance TYK page 277 Q1-4

Human Homeostasis Can you do it? Know how the water concentration of the blood is maintained. Explain the role of ADH in osmoregulation Know how the blood sugar concentration is maintained. Explain the role of insulin, glucagon and adrenaline in controlling blood sugar levels.