Homeostasis in Mammals

Homeostasis in Mammals

• Homeostasis is the maintenance of a stable internal environment.
• Organisms evolved to perform specialist functions, leading to interdependence of cells.
• Coordination systems (nervous and endocrine) are crucial for this.
• The internal environment (extracellular fluids) surrounds cells, providing nutrients and removing waste.
• Homeostasis ensures cells function despite external changes.
• Homeostasis maintains normal ranges of chemical composition, volume, and other features of blood and tissue fluid, allowing cells to operate normally.
• Homeostasis involves continuous fluctuations around a set point.

Importance of Homeostasis

• Enzymes and proteins are sensitive to pH and temperature changes.
• Variations affect enzyme efficiency or cause denaturation.
• Changes to membrane proteins affect substance transport across cell membranes.
• Water potential fluctuations cause cell shrinkage/swelling, hindering normal cell functions.

Control Mechanisms and Feedback

• Set point: Desired level of operation regulated by receptors.
• Receptor: Detects internal or external stimuli, signaling deviations from set point.
• Central Control: Coordinates information from various sources.
• Effector: Initiates actions to return the system to the set point.
• Feedback loop: Informs the receptor of the changes brought about by the effector.
• Negative feedback systems return the system to the set point rather than move further away from it.
• Positive feedback systems amplify a response.

Excretion and Kidney Structure

• Excretion: Removal of waste products of metabolism.
• Elimination: Removal of substances that weren't involved in metabolism (e.g., dietary fiber).
• Carbon Dioxide (CO2) and water are major excretory products of respiration.
• Urea is a nitrogenous waste product.
• Urea is produced in the liver from excess amino acids via deamination.
• Ammonia is a toxic byproduct of deamination, converted to urea.
• Three stages produce urea: Ammonia to ammonia/ urea to urea cycle.
• Other excretory substances: bile pigment, mineral salts.

Kidney Structure

• Fibrous capsule: Outer membrane protecting the kidney.
• Cortex: Outer region containing renal capsules, convoluted tubules, and blood vessels.
• Medulla: Inner region with loops of Henle, collecting ducts, and blood vessels.
• Renal pelvis: Funnel-shaped cavity collecting urine into the ureter.
• Ureter: Tube carrying urine to the bladder.
• Renal artery: Supplies blood to the kidney.
• Renal vein: Returns blood from the kidney.
• Nephrons: The functional units of the kidney, microscopic, tubular structures.

The Structure of the Nephron

• Renal (Bowman's) capsule: Cup-shaped structure surrounding the glomerulus.
• Glomerulus: Knot of capillaries filtering blood.
• Proximal convoluted tubule: Tubular structure with microvilli increasing surface area.
• Loop of Henlé: Hairpin-loop extending into the medulla.
• Distal convoluted tubule: Tubular structure with fewer capillaries compared to the proximal tubule.
• Collecting duct: Wide tube merging into the renal pelvis.
• Afferent arteriole: Vessel supplying blood to the nephron.
• Efferent arteriole: Vessel draining blood away from the nephron.
• Peritubular capillaries: Network around the tubules, reabsorbing substances.

Kidney Function – Ultrafiltration and Selective Reabsorption

• Ultrafiltration: High pressure forcing water, glucose, mineral ions, and other small molecules through the glomerulus, forming the glomerular filtrate.
• Selective reabsorption: Recovering useful substances (water, glucose, salts), from filtrate back into the blood stream in the proximal convoluted tubule and other parts of the nephron using active transport and diffusion.

Control of Water and Solute Concentration of the Blood

• Osmoregulation: Maintaining constant water and solute levels in the blood, using hormones.
• Osmoreceptors: Sensory cells detect changes in water potential in the blood.
• Antidiuretic hormone (ADH): Hormone secreted by the posterior pituitary, increasing water permeability in collecting ducts, returning water to the blood and producing concentrated urine.
• Osmoregulation is a feedback system reacting to changes in blood water potential.

Hormones and the Endocrine Glands

• Hormones: Chemical messengers secreted by endocrine glands and transported in the blood.
• Target cells: Cells with receptors to receive and respond to specific hormones.
• Cyclic AMP (second messenger system): Series of reactions amplifying a signal.
• Example: Adrenaline stimulating liver cells to convert glycogen into glucose.

Regulation of Blood Glucose

• Normal blood glucose concentration.
• Three sources: Direct from diet, breakdown of glycogen, gluconeogenesis.
• Insulin lowers blood glucose: Increasing cellular respiration, promoting glycogen formation.
• Glucagon raises blood glucose.
• Adrenaline: Increases blood glucose in times of stress or excitement.
• These hormones work antagonistically in a negative feedback system to regulate blood glucose.

Biosensors

• Biosensors: Devices using biological molecules (enzymes or antibodies) to detect specific chemicals.
• Example: Urine analysis for glucose, protein, and ketones can aid in diagnoses.