Homeostasis and Negative Feedback

• Homeostasis is the maintenance of a constant internal environment.
• This ensures the internal environment, like blood and tissue fluids, remains within narrow limits.
• Homeostasis maintains body temperature, water potential, and blood glucose concentrations.
• It allows organisms to be independent from external environmental changes.

Homeostasis and Negative Feedback

• When changes are detected internally or externally, the body initiates corrective mechanisms in response to a stimulus.
• These mechanisms aim to reverse the effect of the stimulus which restores normal conditions, sending feedback to a receptor to halt the corrective mechanism.
• The negative feedback process involves change detection, receptor cell detection, a sequence of corrective events, and then a return to normal levels.
• Restoring the normal level triggers feedback to the receptor to cease the corrective actions.

Homeostatic Control of Body Temperature

• The skin plays a role in regulating body temperature
• The skin contains:
  • Blood capillaries
  • Hair follicles
  • Sebaceous glands
  • Arterioles:
    • Hair papilla
    • Layers of epidermis/dermis

Increased Body Temperature

• Sweat glands become more active, producing more sweat.
• Sweat is sent through sweat ducts and secreted onto the skin surface.
• Latent heat is lost when water in sweat evaporates.
• Vasodilation of skin arterioles increases blood flow to the capillaries under the skin, resulting in heat loss via conduction, convection, and radiation.
• Hair erector muscles relax, allowing hair to lie closer to the skin, trapping a thin layer of air, enabling heat loss.
• Decrease in metabolic rate, decreases heat release.

Decreased Body Temperature

• Sweat glands become less active, reducing sweat production.
• Less evaporation occurs, minimizing latent heat loss.
• Vasoconstriction of skin arterioles reduces blood flow to capillaries, limiting heat loss through conduction, convection, and radiation.
• Hair erector muscles contract, erecting hairs and trapping a thicker layer of air, reducing heat loss.
• Metabolic rate increases, consequently increasing heat release.
• Shivering occurs through spasmodic contraction of skeletal muscles.
• The rate of respiration increases, releasing more heat energy.

Hormonal Homeostatic Control

• Hormones regulate blood glucose and water potential.
• When blood glucose rises above normal, insulin is released.
• When blood glucose decreases below normal, glucagon is released.
• Less ADH is released when water potential in the blood increases above normal.
• More ADH is released when water potential in the blood decreases below normal.

Hormones

• Hormones are chemical substances produced in small amounts by endocrine glands.
• They are transported in blood to target organs, where exerting specific effects.
• After exerting effects, hormones are broken down in the liver and excreted by the kidneys.
• Hormones act as chemical messengers influencing growth and development.

Endocrine Glands

• Endocrine glands release secretions directly into the bloodstream
• Exocrine glands secrete substances into ducts.
• An exocrine gland:
  • Salivary glands secrete saliva.
  • The pancreas secretes pancreatic juice through the pancreatic duct.
• An endocrine gland:
  • Islets of Langerhans (pancreas) secrete insulin and glucagon.
  • The pituitary gland secretes ADH.
  • Ovaries secrete oestrogen and progesterone.
  • Testes secrete testosterone.

Insulin

• Stimulus: High blood glucose concentration
• Receptor: Islets of Langerhans in the pancreas
• The islets of Langerhans secrete more insulin into the bloodstream.
• Blood transports the insulin to the liver and muscles.
• Insulin increases cell membrane permeability to glucose, increasing glucose absorption by cells.
• Insulin increases the rate of respiration.
• The liver and muscles convert excess glucose to glycogen for storage.
• Result: Blood glucose lowers, providing negative feedback to reduce insulin production

Glucagon

• Stimulus: Low blood glucose concentration.
• Islets of Langerhans in the pancreas are the receptors
• Islets of Langerhans secrete glucagon into the bloodstream.
• Blood transports the glucagon to the liver and muscles.
• Glucagon converts stored glycogen back to glucose.
• Glucose from the liver enters the bloodstream.
• As a result blood glucose rises, which provides negative feedback to reduce glucagon production.

Diabetes Mellitus

• Diabetes Mellitus is a medical condition characterized by persistently higher than normal blood glucose.
• Type 1 diabetes:
  • Can develop at any age, often referred to as juvenile or insulin-dependent diabetes.
  • Islets of Langerhans in the pancreas fail to produce sufficient insulin.
• Type 2 diabetes:
  • Typically a late-onset condition.
  • Target cells (liver and muscle cells) become less responsive to insulin.

Risk Factors of Diabetes Mellitus

• Obesity
• Age: The risk increases with age.
• Family history: The risk is higher if family members are affected.
• Blood lipids level with higher levels of low-density cholesterol.
• Lifestyle (higher risk if inactive).

Treatment of Diabetes Mellitus

• Constant monitoring of blood glucose and urine is key.
• Diet must be monitored.
• Regular medication.
• Insulin injections (Type 1).
• Leading a healthy lifestyle is required, including exercise, diet, and weight management.