APC 11- homeostasis 1

define homeostasis , why is it vital for normal body function , explain the concepts of the homeostatic range, principles of negative and positive feedback , key examples of homeostatic processes , and understand how disruption of homeostasis leads to disease

What is homeostasis ?

• The maintenance of a relatively stable internal environment despite a changing external environment and varying internal activity, using negative feedback mechanisms.

• keeping the body’s precise internal conditions within a set range, despite internal or external environmental fluctuations

• each system/ cells has a range - they can still work within that range higher or lower , when outside the range - no longer function

What are some examples of physiological ranges ?

What are vital signs?

• ‘Vital signs’ provide valuable insight into a patient's condition, including how they are responding to medical treatment and, importantly, whether the patient is deteriorating

• Early changes in vital signs often signal deterioration before symptoms become clinically obvious

How does the body maintain homeostasis ?

• the nervous system ( brain ) - neural control 

• the endocrine system - endocrine control 

What are the structures involved in the neural control ?

Hypothalamus

• Temperature control

• Water balance (through

• Antidiuretic Hormone (ADH)

Medulla oblongata (part of brainstem)

Important vital signs:

• Breathing

• Heart rate

• Blood pressure •

Chemosensors for CO2

What structures are involved in endocrine control ?

Some examples:

• Pituitary gland – several hormones (master regulator)

• Pineal gland – melatonin (sleep/wake)

• Adrenal gland (aldosterone)

• Pancreas (insulin and glucagon)

• Thyroid gland (thyroid hormone; calcitonin)

• Parathyroid glands (parathyroid hormone)

What is the negative feedback loop ?

• if the variable is disturbed , this system restores it towards it set point value 

What Are some examples of negative feedback ?

• Body temperature (thermoregulation)

• Blood osmolality (osmoregulation)

• Blood glucose (glucoregulation)

and many more

What is thermoregulation ?

the homeostatic process by which organisms maintain a stable internal core body temperature within a narrow, optimal range for enzymatic function, typically around 37°C (98.6°F) in humans

What is osmoregulation ?

• the process of maintaining the balance of water and mineral salts in the body's fluids, a key part of homeostasis. It is vital for cells to function properly, as cells can burst or shrivel if they lose or gain too much water through osmosis

• Osmolarity here means the amount of solutes dissolved in the blood

  An increase in blood osmolarity means the concentration of solutes gets higher

  This is due to a decrease in the amount of water in the blood, usually due to dehydration

What is glucoregulation ?

• the physiological process that maintains stable blood glucose (sugar) levels through the coordinated action of hormones, primarily insulin and glucagon, released by the pancreas

too high - beta receptors

too low - alpha receptors

• Glycolysis: The breakdown of glucose into pyruvate to produce energy (ATP).

• Glycogenesis: The synthesis of glycogen from excess glucose for storage, primarily in the liver and muscle cells, stimulated by insulin.

• Glycogenolysis: The breakdown of stored glycogen into glucose, which is then released into the bloodstream to raise blood sugar levels, stimulated by glucagon during fasting or exercise.

• Gluconeogenesis: The production of new glucose from non-carbohydrate sources (such as amino acids and glycerol from fats), mainly in the liver and kidneys, a process stimulated by glucagon and cortisol during prolonged fasting.

`Why do we need to keep blood glucose concentration constant ?

Hyperglycaemia:

• Damages microvasculature:

• Eyes: retinopathy

• Kidneys: nephropathy

• Nerves: neuropathy

• Damages macrovasculature (lining of arteries)

Hypoglycaemia

• Damages brain – reduced cognition, coma, death

What is positive feedback loop ?

• It has the opposite action to a negative feedback loop

• A positive feedback loop MAGNIFIES the original response instead of correcting it

examples -

During blood clotting, the stimulus

(wound) activates a cascade which

rapidly accelerates blood clotting

During childbirth, stretching of the

cervix leads to more stretching, not less

summary 

• Homeostasis is defined as ‘The maintenance of a relatively stable internal environment despite a changing external environment and varying internal activity, using negative feedback mechanisms’.

• Homeostasis is involved in thermoregulation, osmoregulation, and glucoregulation

• The nervous and endocrine systems work together to maintain homeostasis