Body Balance Guide

Cheatsheet Content

### Overview This cheatsheet summarizes key concepts in body balance, including thermoregulation, osmoregulation, kidney anatomy, renal failure, and dialysis. #### Key Points - Understand how the body maintains a stable internal environment through feedback loops. - Learn the roles of the hypothalamus, ADH, and aldosterone in temperature and water balance. - Explore kidney structure, urine formation, and common disorders like kidney stones and renal failure. - Review how excretion works and the difference between hemodialysis and peritoneal dialysis. ### Homeostasis **Definition:** Maintenance of a constant internal environment of an organism despite changes in the external environment. - **Internal environment:** Fluid surrounding cells (blood, tissue fluid, lymph). - Cells depend on this milieu; any change impairs function. #### Why homeostasis matters 1. **Enzyme activity:** Each enzyme has optimal temperature & pH; deviations cause denaturation or loss of shape. 2. **Cellular survival:** Semi-permeable membranes; abrupt shifts in water, salts, or temperature lead to swelling, shrinkage, or death. 3. **Metabolic balance:** All biochemical reactions require correct concentrations, temperature, and pH. #### Features of homeostasis - **Dynamic:** Conditions fluctuate within narrow limits. - **Self-regulating:** Corrections occur automatically. - **Feedback-driven:** Chiefly negative feedback. #### Components of a homeostatic control system | Part | Definition | Typical examples | Role | |-------------|-------------------------------------------|--------------------------------------|--------------------| | **Receptor** | Detects change in internal/external milieu | Thermoreceptors, chemoreceptors | Senses stimulus | | **Coordinator** | Receives receptor signals, decides response | Brain, hypothalamus, endocrine glands | Decision making | | **Effector** | Executes corrective action | Sweat glands, muscles, kidneys | Implements response | #### Negative feedback (key mechanism) A process where the effect produced reduces or opposes the original stimulus. - **Temperature control:** Heat $\rightarrow$ receptors $\rightarrow$ hypothalamus $\rightarrow$ sweat glands $\rightarrow$ cooling. - **Blood glucose:** $\uparrow$Glucose $\rightarrow$ insulin $\rightarrow$ uptake by cells $\rightarrow$ $\downarrow$Glucose; $\downarrow$Glucose $\rightarrow$ glucagon $\rightarrow$ release from liver. #### Consequences of failure - Enzyme malfunction, metabolic disorders, diseases (diabetes, dehydration, heat stroke), cell death. ### Thermoregulation **Definition:** Process by which organisms maintain body temperature within a normal range despite environmental temperature changes. #### Importance - Keeps enzymes functional (prevents denaturation or slowed activity). - Protects against heat stroke and hypothermia. #### Organism categories | Type | Definition | Examples | Key features | |------------------|-------------------------------------------|------------------------|----------------------------------| | **Poikilotherms** (cold-blooded) | Body temperature follows environment | Fish, frog, lizard, snake | No internal temperature control | | **Homeotherms** (warm-blooded) | Maintains constant body temperature | Humans, birds, mammals | Strong thermoregulation, $\approx 37 \,^\circ\text{C}$ in humans | #### Human thermoregulation (hypothalamic control) ##### When temperature rises 1. **Receptors:** Skin & blood thermoreceptors detect heat. 2. **Coordinator:** Hypothalamus processes signals. 3. **Effectors:** - **Sweating:** Evaporation cools skin. - **Vasodilation:** Peripheral vessels widen, increasing heat loss. - **Reduced metabolic heat production.** ##### When temperature falls (Cold Response) **Cold-induced thermoregulation:** The coordinated physiological events that raise body temperature when ambient temperature falls. 1. **Receptors:** Cold-sensitive thermoreceptors in skin & deep tissues detect a drop in temperature. 2. **Coordinator:** Hypothalamic pre-optic area receives the signal and activates the cold-defense centre. 3. **Effectors:** - **Shivering:** Rapid muscle contractions generate heat through ATP hydrolysis. - **Vasoconstriction:** Sympathetic stimulation narrows peripheral blood vessels, reducing heat loss. - **Increased metabolic rate:** Thyroid hormones and catecholamines boost basal metabolism, producing additional heat. - **Result:** Core temperature is restored to the normal set-point ($\approx 37 \,^\circ\text{C}$). #### Comparison table (temp regulation) | Condition | Blood vessels | Sweat | Metabolism | |-----------|----------------|-------|------------| | Hot | Vasodilation | Yes | Decreases | | Cold | Vasoconstriction | No | Increases | #### Failure outcomes - **Heat stroke:** Excessive heat, sweating stops. - **Hypothermia:** Severe cold, enzymes slow, can be fatal. ### Osmoregulation **Definition:** Regulation of water and salt balance in the body. #### Why essential - Prevents cell lysis (excess water) or plasmolysis (insufficient water). - Maintains proper conditions for metabolic reactions. - Controls blood volume & blood pressure. #### Strategies in different environments ##### Freshwater animals (e.g., freshwater fish) - **Problem:** Body fluids more concentrated $\rightarrow$ water influx. - **Adaptations:** 1. Do not drink water. 2. Produce large volumes of dilute urine. 3. Actively absorb salts through gills. ##### Marine animals (e.g., sea fish) - **Problem:** Body fluids less concentrated $\rightarrow$ water loss. - **Adaptations:** 1. Drink seawater. 2. Excrete excess salts (gills/kidneys). 3. Produce small volume of concentrated urine. ### Human Osmoregulation – Kidney Focus #### Kidneys (primary organ) - **Functions:** Filter blood, regulate water & salt, eliminate nitrogenous wastes. #### Nephron (basic functional unit) - **Components:** Renal corpuscle (glomerulus + Bowman's capsule) $\rightarrow$ Renal tubule (PCT, Loop of Henle, DCT, collecting duct). #### Hormonal control (Antidiuretic Hormone - ADH) | Condition | ADH Level | Renal Effect | Net Result | |----------------------------------|-----------|----------------------------------------------------|----------------------------| | Low body water (high plasma osmolality) | $\uparrow$ ADH | $\uparrow$ Water reabsorption in collecting duct (via aquaporin-2 insertion) | Concentrated urine, water conserved | | High body water (low plasma osmolality) | $\downarrow$ ADH | $\downarrow$ Water reabsorption $\rightarrow$ dilute urine | Excess water eliminated | - **Source:** Synthesized in the hypothalamus, stored in the posterior pituitary. - **Key point:** ADH acts via **negative feedback** - the restored water balance reduces ADH secretion. #### Hormonal control (Aldosterone) - **Origin:** Adrenal cortex (zona glomerulosa). - **Stimuli:** Low plasma Na$^+$, low blood pressure, or $\uparrow$ renin-angiotensin-II. - **Action:** Increases Na$^+$ reabsorption (and consequently water) in the distal convoluted tubule and collecting duct; promotes K$^+$ excretion. #### Integrated Feedback Loop 1. $\downarrow$ Water $\rightarrow$ $\uparrow$ Plasma Osmolality $\rightarrow$ ADH released $\rightarrow$ Collecting duct becomes permeable $\rightarrow$ Water reabsorbed $\rightarrow$ Plasma osmolality $\downarrow$ $\rightarrow$ ADH secretion falls. 2. $\downarrow$ Na$^+$ or $\downarrow$ Blood Pressure $\rightarrow$ Renin-angiotensin-II rises $\rightarrow$ Aldosterone secreted $\rightarrow$ Na$^+$ (and water) reabsorption $\uparrow$ $\rightarrow$ Volume and pressure restored $\rightarrow$ Aldosterone secretion declines. #### Disorders - **Dehydration:** Excess water loss (diarrhea, sweating). - **Overhydration:** Excess water intake, dilution of body fluids. ### Excretion in Humans **Definition:** Removal of nitrogenous and other metabolic wastes from the body. #### Main waste products | Waste | Source | |-----------------------|---------------------------| | Urea | Protein catabolism | | Uric acid | Nucleic acid breakdown | | Creatinine | Muscle metabolism | | Excess salts & water | Metabolic processes | #### Urinary system organs - Kidneys, ureters, urinary bladder, urethra. #### Kidney anatomy (quick reference) - **Shape:** Bean-shaped. - **Size:** $10-12$ cm long, $5-7$ cm wide, $3$ cm thick; $\approx 150$g each. - **Position:** One on each side of vertebral column; right kidney slightly lower (liver). ##### Internal regions 1. **Cortex:** Contains glomeruli & Bowman's capsules. 2. **Medulla:** Contains loops of Henle & collecting ducts. 3. **Pelvis:** Funnels urine to ureter. #### Urine formation (three steps) ##### 1. Ultrafiltration (Renal Corpuscle) - **Location:** Glomerulus within Bowman's capsule. - **Driving force:** Net filtration pressure $\approx 60$ mm Hg (glomerular hydrostatic pressure - Bowman's capsule hydrostatic pressure – oncotic pressure). - **Filtered solutes:** Water, urea, glucose, amino acids, Na$^+$, Cl$^-$, and small metabolites. - **Retained:** Proteins, cells, and large plasma proteins (e.g., albumin). ##### 2. Selective Reabsorption (Renal Tubule) | Segment | Primary Reabsorbed Substances | Approx. % Recovered | |-------------------------------------|--------------------------------------------------------|---------------------| | Proximal Convoluted Tubule (PCT) | Glucose (100%), amino acids, Na$^+$, Cl$^-$, HCO$_3$$^-$, most water | Near-complete | | Loop of Henle (descending) | Water (via osmosis) | Variable | | Loop of Henle (ascending) | Na$^+$, K$^+$, Cl$^-$ (active) | $-$ | | Distal Convoluted Tubule (DCT) | Na$^+$, Cl$^-$ (regulated by aldosterone) | $-$ | | Collecting Duct | Water (regulated by ADH) | $-$ | ##### 3. Tubular Secretion - **Sites:** Primarily DCT and collecting duct. - **Substances added to tubular fluid:** H$^+$ (acid-base balance), K$^+$, drug metabolites, creatinine, and other organic acids. #### Hormonal Modulation - **ADH:** Enhances water reabsorption in the collecting duct $\rightarrow$ concentrated urine. - **Aldosterone:** Promotes Na$^+$ (and water) reabsorption in DCT/collecting duct $\rightarrow$ expands extracellular fluid volume. #### Micturition (Urination) **Definition:** The reflexive and voluntary expulsion of urine from the urinary bladder. 1. **Storage phase:** - Detrusor muscle (bladder wall) relaxed. - Internal urethral sphincter (smooth muscle) contracted. 2. **Voiding phase:** - Stretch receptors in bladder wall activate the pontine micturition center. - Parasympathetic outflow (pelvic nerves) causes detrusor contraction. - Internal sphincter relaxes; external sphincter (skeletal muscle) is voluntarily relaxed. 3. **Outcome:** Urine is expelled through the urethra. ### Kidney Disorders #### Kidney Stones (Renal Calculi) **Definition:** Hard crystalline mass formed in the kidney from precipitated salts/minerals. ##### Types & prevalence | Type | Approx. % | Typical cause | |-------------------|-----------|-----------------------------------------------------| | Calcium oxalate | $70-80\%$ | Low water intake, excess Ca$^{2+}$/oxalate, high vitamin D | | Uric acid | $10-15\%$ | High-protein diet, gout, acidic urine | | Struvite | $\approx 10\%$ | Bacterial infection (magnesium ammonium phosphate) | | Cystine | $1-2\%$ | Genetic disorder (cystinuria) | ##### Major causes - Dehydration, high salt/mineral concentration, poor diet, infections, genetic factors. ##### Clinical features - Severe flank pain (renal colic), radiation to abdomen/groin, hematuria, dysuria, nausea/vomiting. ##### Management - **Small stones:** High fluid intake, analgesics, spontaneous passage. - **Large stones:** Lithotripsy (shock-wave fragmentation) or surgical removal. - **Prevention:** Adequate hydration, balanced diet, reduced salt intake. #### Kidney Failure (Renal Failure) **Definition:** Inability of kidneys to filter blood and remove metabolic wastes. ##### Types - **Acute renal failure:** Sudden, often reversible; causes include severe dehydration, infection, toxins. - **Chronic renal failure:** Progressive, usually irreversible; major causes are diabetes, hypertension, long-term kidney disease. ##### Symptoms - **Early:** Fatigue, oliguria (reduced urine), peripheral edema. - **Advanced:** Uremia, hypertension, anemia, dyspnea. ##### Complication – Uremia - Accumulation of urea in blood due to inadequate filtration. ##### Treatment options 1. **Renal dialysis:** Temporary artificial purification (see below). 2. **Kidney transplant:** Permanent solution; preferred definitive therapy. ### Renal Dialysis **Definition:** Artificial process that removes metabolic wastes, excess salts, and water from blood when kidneys fail. #### Why needed - Kidneys cannot eliminate urea and toxins $\rightarrow$ toxic blood, disturbed homeostasis. #### Principle - Relies on **diffusion** and **convection** across a semi-permeable membrane. #### Types ##### Hemodialysis | Aspect | Description | Key steps | Advantages | Disadvantages | |---------------|-------------------------------------------|------------------------------------------------------|-----------------|----------------------------------------------| | **Hemodialysis** | Blood passes through a dialyzer (artificial kidney). | 1. Blood drawn from artery $\rightarrow$ dialyzer. 2. Diffusion of urea, salts into dialysis fluid. 3. Clean blood returned to vein. | Rapid waste removal. | Requires hospital, expensive, infection risk. | ##### Peritoneal dialysis | Aspect | Description | Key steps | Advantages | Disadvantages | |------------------|-----------------------------------------|------------------------------------------------|----------------|-------------------------------------| | **Peritoneal dialysis** | Peritoneum acts as membrane; dialysis fluid infused into abdominal cavity. | 1. Fill cavity with fluid. 2. Waste diffuses into fluid. 3. Fluid drained and replaced. | Can be done at home; no machine. | Slower, peritonitis risk. | #### Comparison: Dialysis vs. Normal Kidney | Aspect | Kidney (natural) | Dialysis (artificial) | |-----------------------|------------------|-----------------------| | Continuity | Continuous | Periodic | | Efficiency | Highly efficient | Less efficient | | Selectivity | Highly selective | Less selective | | Hormone production | Yes | No | | Blood pressure regulation | Yes | No | #### Limitations - Cannot replace hormonal functions or fully regulate blood pressure; lifelong therapy unless transplant performed. ### Disorders Linked to Osmoregulation & Excretion | Disorder | Primary Osmoregulatory Defect | Typical Clinical Feature | |-------------------------------------|-------------------------------------------------------------------------|-----------------------------------------------------------| | **Dehydration** | Inadequate water intake or excessive loss $\rightarrow$ $\uparrow$ ADH, concentrated urine | Thirst, dry mucous membranes, high plasma osmolality | | **Overhydration (Water Intoxication)** | Suppressed ADH $\rightarrow$ excess water excretion, but if ADH remains high, hyponatremia develops | Nausea, headache, seizures (low Na$^+$) | | **Hyponatremia** | Excess water relative to Na$^+$, often from ADH dysregulation | Confusion, lethargy, cerebral edema | | **Hypernatremia** | Water loss exceeding Na$^+$ loss, inadequate ADH response | Neurological deficits, thirst, high plasma Na$^+$ | ### Integrated Review – Linking Homeostasis Themes - **Osmoregulation** safeguards cells from lysis (excess water) and plasmolysis (insufficient water) and is orchestrated mainly by the kidneys under hormonal control. - **Thermoregulation** (hypothalamic negative feedback) and **osmoregulation** (renal-ADH/aldosterone feedback) are parallel examples of how the body detects a deviation, processes the information centrally, and activates effectors to restore the set-point. - Both systems rely on **receptors** $\rightarrow$ **coordinator** $\rightarrow$ **effectors** architecture introduced in the Homeostasis section. - Failure of either system (heat stroke, hypothermia, dehydration, overhydration) disrupts overall homeostasis and can precipitate secondary disorders such as **renal failure** or **uremia**, underscoring the interconnected nature of the physiological networks covered.