Homeostatic control of blood glucose

Blood glucose

Necessary for cellular respiration, blood is transport system that brings glucose to all tissues so it can move into cells as needed (through concentration gradient)

Abnormally low glucose

Cells of tissue (skeletal muscle, heart muscle, brain etc.) cannot do cellular respiration and are starved of energy

Abnormally high glucose

Causes dehydration of tissues, as water moves out of cells into blood via osmosis

Causes of blood sugar increasing

Carbs are broken down into glucose in digestive system, absorbed into blood via enterocytes

Causes of blood sugar decreasing

After exercise and periods of fasting, glucose moves from blood into muscles/tissues causing low blood glucose

Regulation of blood sugar

Glucose is stored as glycogen (chains of glucose molecules) in liver and muscle cells

Role of liver

Liver converts glucose into glycogen for storage, or glycogen into glucose for release into bloodstream. Liver has first chance to absorb nutrients from undigested food

Process of glucose in liver

- Absorbed into capillaries of villi in small intestine, hepatic portal vein carries glucose to liver

Glucose either:

Gets removed from blood to provide energy for liver functioning, removed from blood by convertin to glycogen, or continues to circulate in the blood for body cells to absorb

Glycogenesis

Conversion of glucose to glycogen (stimulated by insulin)

Glycogenolysis

If more glucose is required, glycogen is converted back into glucose (stimulated by glucagon)

Gluconeogenesis

Fats and proteins are used to make glucose

Insulin

Decreases blood sugar by

- accelerating transport of glucose from blood into cells

- accelerating conversion of glucose into glycogen

- stimulating conversion of glucose into fat in adipose tissue and ATP for protein synthesis

Glucagon

Increases blood sugar levels by stimulating glycogenolysis and glucaneogenesis (involved process of lipolysis where lipids are broken down) can also have a mild stimulating effect on protein breakdown

Alpha cells of Islets of Langerhans

Secrete glucagon

Beta cells of Islets of Langerhands

Secrete insulin

Adrenal cortex

Secretes glucocorticoids (cortisol), stimulated by ACTH from pituitary.

- Regulates carbohydrate metabolism by ensuring enough energy is provided to cells

- stimulates conversion of glycogen to glucose,

- increases rate of amino acids being removed from muscle cells/adipose tissue and transported to liver (some converted to glucose)

Adrenal medulla

Secretes adrenaline and noradrenaline

- elevates blood glucose level through glycogenolysis,

- stimulates production of lactic acid from glycogen in muscle cells which can be used by liver to make glucose