Homeostasis Part 1

Homeostasis Part 1

• Homeostasis is the maintenance of a constant internal environment.
• It's a physiological process, characteristically stable, in higher vertebrates.
• Claude Bernard (1850s) was a French physiologist who established that multicellular organisms have an internal environment that can constantly be changed to maintain cellular function.
• An organ can adjust blood composition to maintain "milieu interieur".
• The body must maintain constant conditions, like pH and temperature, inside, despite outer conditions changing.
• Enzymes only function within specific temperature ranges.
• pH changes in tissues affect enzyme reactions within those cells.
• Changes in water potential can damage or burst cells.
• Homeostasis allows organisms to live in diverse habitats, better control metabolic needs, and make metabolism more efficient and economical.
• Essential body parts that need to be regulated: body temperature, blood pressure, blood pH, oxygen/carbon dioxide concentration, osmoregulation (water balance), and blood glucose.

How Homeostasis Works

• Homeostasis is maintained through stimuli, receptors, regulatory mechanisms, and effectors/response.
• A stimulus is a change in the internal environment.
• Receptors identify the stimulus.
• An automatic, self-regulatory system corrects the change in the environment.
• Effectors/organs/tissues react to bring about the correction.
• Response: Negative feedback. The body does the opposite to bring back to normal function.

Negative Feedback Example: Water Potential

• An increase in blood water potential (a stimulus) is detected by osmoreceptors (receptors).
• Your body responds by return the water osmolality to the normal condition.

Negative Feedback

• The body reverses the change.
• This is common in biological systems.
• Multiple systems are required for homeostasis.
• The body's organs and systems provide cells with their basic needs.

Regulation of Body Temperature

• The main organ involved in body temperature regulation is the skin.
• The skin acts as a: protective covering, excretory organ, and regulator of body temperature.
• Changes in environmental temperature can be detected by the skin.

Skin

• The skin has Hair, Sebaceous Glands, Sensory Nerve Endings, Sweat Glands, Muscle, Epidermis, Dermis, Subcutaneous Tissue, Capillaries and Arterioles, Fat, Collagen and Fibroblasts.
• Blood vessels bring oxygen to cells in the skin.
• Blood vessels can dilate or constrict to regulate blood flow through the skin, maintaining temperature.
• Sweat glands produce sweat to cool the body.
• Hair traps air to insulate the body.
• Nerve endings (thermoreceptors) detect changes in external temperature.
• Fatty/adipose tissue insulates the body, preventing heat loss.

Heat Production and Loss

• Metabolic activities (e.g., tissue respiration) produce body heat.
• Liver and muscles are major heat-producing organs.
• Heat can be gained by eating hot food, from the sun, warm air, and exercise.
• Heat loss occurs in two steps: conduction of heat from deeper organs to the skin then transferring heat from skin to surroundings via Radiation, Conduction, Evaporation (27%), Convection (2%), Urination and Defecation (1%).

How Body Temperature is Controlled (Homeostasis).

• Body temperatures are monitored and controlled by temperature receptors in the skin and brain.
• Receptors detect changes in blood temperature flowing through the areas.
• The thermoregulatory centre in the brain is the hypothalamus.
• If the body temperature deviates from 37°C, the hypothalamus and skin receptors send signals, causing actions to raise or lower temperature.

Regulation of Body Temperature – Hypothalamus

• Hypothalamus monitors and regulates body temperature.
• It receives temperature changes from the external environment by receptors in the skin.
• The hypothalamus has a set point at 37.5 ± 0.5°C.
• It monitors blood temperature that passes through it.

Temperature Regulation Mechanisms (Homeostasis).

• Autonomic: vasodilation and vasoconstriction of blood vessels.
• Somatic: shivering.
• Endocrine: hormones like thyroxine and adrenaline.
• Behavioral: clothing, movement.

Regulating Body Temperature - On a Hot Day

• Stimulus: Blood and skin temperatures rise. Receptor: Temperature receptors detect changes and send nerve impulses to the brain.
• Blood vessels dilate, increasing blood flow to the skin, increasing heat loss.
• Sweat production increases, which evaporates, increasing heat loss.
• Hair erector muscles relax, lowering insulation.

Regulating Body Temperature - On a Cold Day

• Stimulus: Blood and skin temperatures fall. Receptor: Temperature receptors detect changes and send nerve impulses to the brain.
• Blood vessels constrict, reducing blood flow to the skin, reducing heat loss.
• Sweat production decreases, decreasing heat loss.
• Hair erector muscles contract, increasing insulation.

Failure of Temperature Regulation

• Hypothermia: core body temperature below 35°C.
• Hyperthermia: abnormally high body temperature due to temperature regulation failure.

Regulation of Blood Glucose

• Liver and pancreas are involved.
• Liver is a storehouse for glycogen.
• Two hormones (glucagon and insulin) control blood glucose levels, secreted from islet cells in the pancreas (islets of Langerhans).
• Glucagon is released by alpha cells.
• Insulin is released by beta cells.

Glucose Homeostasis - Hormone Action

• Insulin converts glucose into glycogen (glycogenesis), storing excess glucose in the liver.
• Glucagon converts glycogen back into glucose (glycogenolysis) when needed.

Glucose Homeostasis

• If glucose levels rise, less glucagon and more insulin is released to convert glucose into glycogen.
• If glucose levels decrease, less insulin and more glucagon is released back into the system to increase blood glucose levels.

What Happens When Glucose Concentration Rises

• Stimulus: Blood glucose concentration increases. Receptor: Islets of Langerhans in pancreas get stimulated.
• The corrective mechanism is to release more insulin, which carries itself in the blood to liver/muscle cells and converts the increased glucose into glycogen (glycogen storage).

What Happens When Glucose Concentration Falls

• Stimulus: Blood glucose concentration decreases. Receptor: Islets of Langerhans in pancreas get stimulated.
• The corrective mechanism is to release more glucagon, which travels in the blood to liver/muscle cells and converts glycogen back into glucose.

Failure of Blood Glucose Regulation

• High blood sugar (hyperglycemia): excessive glucose in the blood, often leading to diabetes mellitus.
• Low blood sugar (hypoglycemia): causes serious issues (seizures, loss of consciousness, coma, or death).

Explore the concept of homeostasis and its crucial role in maintaining a constant internal environment in higher vertebrates. Learn about the physiological processes involved, the historical perspective provided by Claude Bernard, and how various body functions stabilize conditions like temperature, pH, and blood composition.