chapter 10 homeostasis

Excretory system functions

Regulates blood pressure, blood osmolarity, acid-base balance, and removes nitrogenous wastes

Path of urine (memory trick)

'Kidney to Ureter to Bladder to Urethra' → K-U-B-U

Kidney anatomy — 3 regions

Cortex (outermost layer), Medulla (within cortex), Hilum (deep medial slit containing renal artery, renal vein, and ureter)

Kidney portal system

Two capillary beds in series: 1) Glomerulus in Bowman's capsule (filtration) 2) Vasa recta surrounding the nephrons (reabsorption/secretion)

Blood flow through the kidney

Renal artery → afferent arterioles → glomerulus (Bowman's capsule) → efferent arterioles → vasa recta → renal vein

Bladder — detrusor muscle

Muscular lining of the bladder; under parasympathetic (involuntary) control; contracts to expel urine

Internal urethral sphincter

Smooth muscle; involuntary control (parasympathetic)

External urethral sphincter

Skeletal muscle; voluntary (somatic) control

3 kidney processes (memory trick)

'FSR' → Filtration (blood → filtrate at Bowman's capsule), Secretion (blood → filtrate elsewhere in nephron), Reabsorption (filtrate → blood)

Filtration — driving forces

Determined by Starling forces: hydrostatic and oncotic pressure differentials between the glomerulus and Bowman's space

Proximal convoluted tubule (PCT)

Site of BULK reabsorption of glucose, amino acids, soluble vitamins, salt, and water; also secretes H⁺, K⁺, ammonia, and urea

Descending limb of loop of Henle

Permeable to WATER but NOT salt; water is reabsorbed as filtrate enters the hyperosmotic medulla; filtrate becomes more concentrated

Ascending limb of loop of Henle

Permeable to SALT but NOT water; salt is reabsorbed passively and actively; filtrate becomes hypotonic compared to blood (diluting segment)

Countercurrent multiplier system

Vasa recta and nephron loop flow in opposite directions; allows maximum water reabsorption by maintaining the osmotic gradient in the medulla

Distal convoluted tubule (DCT)

Responds to aldosterone; site of salt reabsorption and waste excretion (similar to PCT but hormonally regulated)

Collecting duct

Responds to both aldosterone AND ADH; variable water permeability allows fine-tuning of water reabsorption based on body needs

Kidney and pH regulation

Selectively reabsorbs or secretes bicarbonate (HCO3⁻) or hydrogen ions (H⁺) to regulate blood pH

Aldosterone — type, source & trigger

Steroid hormone; regulated by the renin-angiotensin-aldosterone system (RAAS); released when blood pressure and volume are LOW

Aldosterone — action & effect

Increases Na⁺ reabsorption in DCT and collecting duct → water follows → increased blood VOLUME; blood osmolarity UNCHANGED

ADH (antidiuretic hormone) — type, source & trigger

Peptide hormone; synthesized in hypothalamus, released by posterior pituitary; triggered by LOW blood volume OR HIGH blood osmolarity

ADH — action & effect

Increases water permeability of collecting duct → more water reabsorbed → increased blood VOLUME and DECREASED blood osmolarity

Aldosterone vs. ADH — key difference (memory trick)

Aldosterone = Volume only (osmolarity unchanged). ADH = Volume AND osmolarity (both corrected). 'Aldo adds volume; ADH also dilutes'

Skin — 3 major layers (memory trick)

HDE from deep to surface: Hypodermis, Dermis, Epidermis

Hypodermis

Deepest layer; contains fat and connective tissue; connects skin to underlying structures; provides insulation

Dermis — 2 layers

Papillary layer (superficial) and reticular layer (deeper); contains sensory receptors, blood vessels, hair follicles, and glands

Epidermis — 5 strata (memory trick)

'Basale Spinosum Granulosum Lucidum Corneum' → 'Before She Gets Laid (in the) Coffin' from deep to surface

Stratum basale

Deepest epidermal layer; contains stem cells; site of keratinocyte proliferation

Stratum spinosum

Cells become interconnected; site of Langerhans cells (antigen-presenting cells)

Stratum granulosum

Keratinocytes die and lose their nuclei; begin forming the barrier

Stratum lucidum

Present only in thick, hairless skin (palms, soles of feet)

Stratum corneum

Outermost layer; dozens of layers of flattened dead keratinocytes; forms barrier against pathogens and prevents fluid/salt loss

Keratinocytes

Predominant cells of the skin; produce keratin for structural strength and barrier function

Melanocytes

Produce melanin, which protects skin from UV-induced DNA damage; melanin is transferred to keratinocytes

Langerhans cells

Special macrophages in the stratum spinosum; function as antigen-presenting cells in immune defense of the skin

Sensory receptors in the dermis (memory trick)

'Merkel's Free Meissner's Ruffini Pacini' → 'My Free Minutes Run Pretty well' → deep pressure/texture, pain/temp, light touch, stretch, deep pressure/vibration

Merkel cells

Located in dermis; respond to deep pressure and texture

Free nerve endings

Respond to pain and temperature

Meissner's corpuscles

Respond to light touch

Ruffini endings

Respond to stretch

Pacinian corpuscles

Respond to deep pressure and vibrations

Thermoregulation

Maintenance of a constant internal body temperature; key function of the skin

Cooling mechanisms (memory trick)

'Sweat and Spread' → Sweating (evaporation draws heat away) + Vasodilation (increases blood flow to skin surface to release heat)

Sweating — nervous control

Sweat glands are innervated by postganglionic cholinergic sympathetic neurons (unusual — sympathetic but uses ACh, not NE)

Warming mechanisms (memory trick)

'Pile, Constrict, Shiver, Insulate' → Piloerection, Vasoconstriction, Shivering, fat Insulation

Piloerection

Arrector pili muscles contract → hairs stand up → trap a layer of warm air near the skin surface

Vasoconstriction (warming)

Reduces blood flow to skin surface → decreases heat loss to the environment

Shivering

Rapid involuntary muscle contractions generate heat through increased metabolic activity

Other skin functions

Barrier against pathogens, prevents dehydration and salt loss from the bod