Homeostasis

HOMEOSTASIS objectives- objective SHEET 3

1.Describe the components of a feedback system – stimulus, receptor, modulator (control centre), effector, response, feedback (negative).

Feedback system- maintains homeostasis

Homeostasis- process of keeping the environment inside the body fairly constant, despite fluctuations in the external environment

Indicates state of equilibrium- internal conditions change and vary, always relatively narrow limits (tolerance limits)

Examples of what need to be regulated- core body temp, pH and conc of dissolved substances in body fluid, conc of glucose in blood

Homeostatic mechanisms- within body maintain homeostasis (independent to external env)

Main sensory and controlling body systems

1.        The Nervous system- works fast

2.        The Hormonal system- usually works slower  

Both operate through feedback systems (mostly negative feedback)

Feedback loop (stimulus response model)- circular situation in which body responds to a change, or stimulus, with the response altering the original stimulus and thus providing feedback.

Can be neg or pos- depends on whether response increases of decreases original stimulus

Negative feedback- when body’s response has effect of reducing or eliminating the stimulus, restoring state (steady)

e.g. if you feel hot your response might be that you begin to sweat and turn on the air conditioner.

Referred to as steady state- control systems as they return to steady state

e.g. feel hot- response begin to sweat, behavioural response- turn on air conditioner

Positive feedback- when body’s response has effect of reinforcing or intensifying the stimulus that caused it. Has no role in homeostasis, few situations where it does.

The intensified stimulus- results in an even greater response so at times

e.g. during childbirth- oxytocin released, causes contractions of uterus and baby’s head pushes on cervix, pituitary triggered to release more oxytocin.

Components of a feedback loop:

• Stimulus- a change in environment that causes the system to operate. (external or internal)

• Receptors- detect the change (stimuli)

• Modulator- a control centre that processes the messages received by receptor and sending message to the effector.

• Effectors- muscles or glands that make necessary adjustments by receiving messages from modulator. Carries out response by counteracting the effect of the stimulus.

• Response- effecters bring about appropriate reaction

• feedback- response changes original stimulus.

Thermoregulation: process of maintaining balance between heat production and heat loss.

Describe how heat is generated in the body.

-              Metabolic processes (cellular respiration)

-              Transfer from the environment

-              Heat gained from surroundings in conduction, convection and radiation

Describe how heat can be lost from the body.

Radiation, conduction and convection from the surroundings. Transfer to the environment. Evaporation of water from the skin/ lungs, warm air breathed out, warm urine/ faeces.

To main this the heat that is gained by the body must be equal to the heat lost by the body

Achieved through thermoregulation

State that the normal body temperature of humans is approximately 36.7⁰C.

36.5-37

Describe the location of the thermoreceptors in the body (both peripheral and central).

PERIPHERAL: Detect change to the external environment and send information to the hypothalamus, Located in skin and some mucous membranes

CENTRAL Detect changes to the internal environment, Located in the hypothalamus, Some others throughout the body also provide information to the hypothalamus.

Describe how heat can be transferred by radiation, conduction and convection.

The large surface area between internal and external environment provided by the skin means it is very important in thermoregulation.

Types of heat transfer

- Conduction- transfer of heat by direct contact between particles

- Convention- transfer of heat by the movement of liquid gas

- Radiation- transfer of heat by infrared radiation being emitted by objects

Explain how evaporation of sweat can lead to cooling the body.

When the sweat droplets evaporate and turn into a gas heat is lost, because energy is needed for process

Describe how the body responds to a fall in body temperature. (Include both physiological* and behavioural responses.)

Behavioural response- way organism reacts or behaves in response to a stimulus. Reflex (involuntary responses) (occur without conscious thought) e.g. pulling hand away, voluntary + learned responses.

Decrease heat production- decrease metabolic rate (long- term), behavioural- decreasing physical activity

Don’t need to include behavioural responses in feedback loop unless question asks

Describe how the body responds to a rise in body temperature. (Include both physiological* and behavioural responses.)

Increase heat loss- vasodilation, sweating, behavioural- turning on/ fan and aircon, removing clothing

Explain the terms vasodilation and vasoconstriction.

Vasodilation (increasing diameter) of blood arterioles in the skin to increase blood flow to the area.

Vasoconstriction- constricting/ decrease in diameter of an arteriole to reduce blood flow to the area.

Decreases heat transfer from internal organs to skin to external env

Describe the relationship between the level of thyroxine and body temperature.

Increase in thyroxine results in an increased body temperature

Decreased thyroxine- decreased body temp.

Explain why piloerection is ineffective in humans as a means of preventing body temperature from falling (goosebumps)

Piloerection- (goosebumps) involves the contraction of small muscles surrounding hair follicles, causing hair to stand erect

Ineffective in humans as we have relatively sparse body hair, as opposed to Furr meaning there is no insulating effect from hair to retain heat.

Explain the relationship between glucose and glycogen.

Glucose- sugar in blood is form of glucose C4H1206, simple carbohydrate, source of energy for cell activities.

Cellular respiration: Glucose + oxygen -> carbon dioxide + water + ATP

Glycogen- glucose is stored as glycogen- which is a complex carbohydrate made up of long chains of glucose molecules

Body can store- 500g of glycogen (liver 100g and skeletal muscle cells 400g)

Can be broken down when required

Glycogen-> glucose- glycogen stored in liver is a short- term energy supply, provides glucose for body cells for approx. 6 hours is no other supply available.

Glycogen stores in liver- available for conversion into glucose to maintain blood sugar levels

Occurs between meals to maintain blood sugar levels

Conversion of glycogen to glucose stimulated by hormone glucagon.

Explain the role of the liver in the regulation of blood sugar

Role of liver- The liver is able to convert glucose into glycogen for storage, or glycogen to glucose for release into the blood

-              Glucose molecules are chemically joined in long chains to form glycogen molecules. This

process, known as glycogenesis, is stimulated by the pancreatic hormone insulin.

Glucose molecules are chemically joined in long chains to form glycogen molecules. This process, known as glycogenesis, is stimulated by the pancreatic hormone insulin.

If the level of glucose in the blood drops below normal, the glycogen stored in the liver and muscle cells can be broken down into glucose. (process called glycogenolysis)

As most of its blood supply travels through hepatic portal- brings blood from stomach, spleen, small and large I.

Glycogen is a short-term energy supply, if more energy is required- the body uses energy reserves in stored fat.

Describe the regulation of blood sugar levels by the hormone’s insulin and glucagon*.

Role of the pancreas- endocrine tissue within the pancreas- specifically the islets of Langerhans, releases hormones responsible for controlling blood glucose levels.

Within the pancreas are clusters of hormone-secreting cells called the islets of Langerhans. The cells in the

islets are of two types:

• alpha cells that secrete glucagon- when chemoreceptors in the islets of Langerhans stimulate those cells to secrete glucagon.

• beta cells that secrete insulin.

Insulin from beta cells- causes a decrease in blood glucose levels by accelerating the conversion of glucose into glycogen in the liver and skeletal muscle (glycogenesis) and stimulating the conversion of glucose into fat (lipids) in adipose tissue, or fat storage tissue, a process called lipogenesis e.t.c.

Glucagon from the alpha cells causes an increase in blood glucose levels. It does this by:

• stimulating glycogenolysis, the conversion of glycogen into glucose, in the liver

• stimulating gluconeogenesis, the production of new sugar molecules from fats (lipids) and amino

acids, in the liver. This involves the breakdown of lipids in a process called lipolysis.

The glucose formed is released Into the blood- blood glucose level rises.

Role of adrenal glands- above the kidneys, medulla + inner portion (adrenaline/ noradrenaline), cortex- outer portion of portion

Adrenaline, noradrenaline and cortisol- Increase blood glucose levels

Define the following terms: glycogenesis, glycogenolysis and gluconeogenesis.

Glycogenolysis- process of converting glucose into glycogen for storage.

Glycogenesis- breaking down glycogen into glucose. lowers blood glucose levels (insulin)

Glucogenesis- creation of new glucose molecules from non-carbohydrate sources, such as amino acids, lactate, and glycerol. raises blood glucose levels.

Describe the effects of adrenalin and cortisol (a glucocorticoid) on blood sugar concentration.

Explain the term hyperglycaemia and the possible causes

Abnormally high glucose levels- hyperglycaemia

Possible causes: poor diet, hormonal changes, pancreatic disorders, stress or illness e.t.c

Distinguish between diabetes type 1 and type 2

Diabetes- disease characterised by abnormally high levels of glucose

Results from body unable to maintain blood sugar level in homeostatic balance

-              Passively thirsty, passing more urine, tired and lethargic, feeling hungry  

Problems: blindness, kidney failure, cardiovascular disease, ulcers and gangrene- requiring amputations of the toes or foot.

Explain how gene therapy and synthetic hormones can be used to treat diabetes mellitus

People with diabetes can be given a synthetic form of insulin which can be used to treat diabetes mellitus.