Homeostasis and Kidney Physiology Vocabulary Flashcards

Vocabulary flashcards covering core principles of homeostasis, renal physiology, hormonal regulation of blood glucose, and plant stomatal mechanisms based on lecture notes.

Homeostasis

The maintenance of a constant internal environment within an organism despite changes in the external or internal environment.

Negative Feedback Mechanism

A homeostatic control mechanism where a change in a factor away from its set point acts as a stimulus, detected by receptors, triggering an effector to perform a corrective action that restores the factor back to the set point.

Positive Feedback Mechanism

A physiological mechanism where a response reinforces and amplifies the original stimulus, such as baby suckling stimulating hormone release (oxytocin and prostaglandin) leading to milk ejection.

Deamination

The breakdown of excess amino acids in the liver to remove the amine group ($\text{NH}_2$), forming toxic ammonia, which is then combined with $\text{CO}_2$ in the urea cycle to produce non-toxic urea.

Ultrafiltration

The non-specific filtration of blood under high hydrostatic pressure in the glomerulus, forcing fluid through capillary endothelium fenestrations, a selective basement membrane barrier (passing molecules smaller than $69000$ RMM), and podocyte slit pores into Bowman's capsule.

Podocytes

Specialized epithelial cells forming the inner layer of Bowman's capsule that feature interdigitating foot processes and slit pores through which glomerular filtrate passes into the capsule lumen.

Selective Reabsorption

The process occurring mainly in the proximal convoluted tubule (PCT) where useful substances such as glucose, amino acids, ions, and water are reabsorbed from the glomerular filtrate back into the capillary blood.

Co-transport (in PCT)

A secondary active transport process on the luminal membrane of PCT cells where sodium ions diffuse into epithelial cells down their concentration gradient, simultaneously carrying glucose or amino acids with them.

Loop of Henle

A hairpin loop extending into the renal medulla that establishes a high solute concentration gradient in the interstitial fluid to enable water reabsorption from the collecting duct into the blood.

Antidiuretic Hormone (ADH)

A hormone produced by hypothalamic neurosecretory cells and released by the posterior pituitary gland that increases the permeability of DCT and collecting duct cells to water by inducing aquaporin insertion.

Aquaporins

Transmembrane channel proteins that facilitate the movement of water molecules across cell surface membranes down a water potential gradient by osmosis.

Cyclic AMP (cAMP)

An intracellular second messenger formed from ATP by adenylyl cyclase upon hormone binding (such as glucagon or adrenaline), which initiates an enzyme cascade.

Glycogenolysis

The enzymatic breakdown of stored glycogen into glucose in liver cells, catalyzed by glycogen phosphorylase in response to hormones like glucagon and adrenaline.

Glycogenesis

The conversion of glucose into stored glycogen in target cells, stimulated by insulin via the activation of the enzyme glycogen synthase.

Gluconeogenesis

The metabolic process of synthesizing glucose from non-carbohydrate sources, such as glycerol and amino acids.

Glucokinase

An enzyme activated by insulin in liver cells that phosphorylates glucose upon entry, trapping it inside the cell.

GLUT4

Glucose transporter proteins stored in cytoplasmic vesicles of adipose and muscle cells that translocate and fuse with the cell surface membrane in response to insulin signal cascades.

Type 1 Diabetes Mellitus

An autoimmune or genetic disorder where pancreatic beta cells fail to produce or secrete insulin.

Type 2 Diabetes Mellitus

A metabolic condition where pancreatic beta cells secrete insulin, but target liver and muscle cells fail to respond properly to circulating insulin, often linked to diet and obesity.

Glucose Biosensor

A portable device containing immobilized glucose oxidase that measures blood glucose concentration by generating an electric current proportional to the glucose oxidation level.

Abscisic Acid (ABA)

A plant stress hormone synthesized during drought that triggers stomatal closure by activating signaling cascades that inhibit proton pumps and cause calcium, chloride, and potassium ion efflux from guard cells.

Guard Cells

Paired specialized epidermal cells surrounding each stoma that regulate pore opening and closing by changing shape according to turgor pressure driven by ion influx/efflux and osmosis.