chapter 24&25

Anatomy & Physiology Study Guide: Chapters 24 & 25

Chapter 24: Fluid, Electrolyte, and Acid-Base Balance

Big Idea

  • Cell function requires a fluid medium with a carefully controlled composition. Alterations can have significant effects on body function.

Three Types of Homeostatic Balance

  • Fluid Balance: Occurs when average daily gains of fluid equal losses.

  • Electrolyte Balance: Occurs when electrolytes ingested equal electrolytes excreted.

  • Acid-Base Balance: Maintained when hydrogen ions (H⁺) are excreted at the same rate they are produced.

Expected Learning Outcomes

  • Fluid Compartments: Name major fluid compartments and explain how water moves between them.

  • Sources and Loss of Water: List the sources of water and routes for water loss.

  • Regulation of Water Intake/Output: Describe mechanisms regulating water intake and output.

  • Conditions of Water Deficiency or Excess: Describe conditions resulting in water deficiency or excess.

  • Physiological Roles of Electrolytes: Understand the roles of sodium, potassium, calcium, magnesium, chloride, and phosphate.

  • Regulation of Electrolytes: Describe the hormonal and renal mechanisms regulating electrolyte concentrations.

  • Buffer Definition and Systems: Define buffers and explain three buffer systems.

  • Pulmonary Ventilation and pH: Discuss how pulmonary ventilation relates to pH of extracellular fluids and the bicarbonate buffer system.

  • Acidosis and Alkalosis: Describe these pH imbalances and their physiological effects.

Total Body Water

  • Definition: Total body water includes all fluids in the body, primarily located in two compartments:

    • Intracellular Fluid (ICF): 65% of body water.

    • Extracellular Fluid (ECF): 35% of body water, including:

    • Tissue (interstitial) fluid: 25%

    • Blood plasma and lymphatic fluid: 8%

    • Transcellular fluid: 2%

    • Example: A young male weighing 70 kg has approximately 40 L of total body water, representing 55-60% of his body weight.

Water Movement Between Fluid Compartments

  • Mechanism: Water moves across capillary walls by capillary filtration into tissue fluid, then across plasma membranes via osmosis.

  • Osmotic Movement: The direction of water movement (into or out of cells) is determined by relative solute concentrations in ICF (potassium) and ECF (sodium).

Sources and Routes of Water Gain and Loss

  • Water Gain: Sources include cellular metabolism (metabolic water) and preformed water (from food and drink).

  • Water Loss: There are two forms:

    • Sensible Loss: Measurable loss (e.g., urine, fecal loss).

    • Insensible Loss: Cannot be measured directly (e.g., cutaneous transpiration).

    • Variability: Water loss can vary based on temperature, humidity, and activity level (e.g., increased loss in cold and hot weather).

Regulation of Water Intake and Output

  • Water Intake Control: Primarily regulated by thirst mechanisms:

    • Thirst is inhibited when salivary glands are signaled by hypothalamic stimulation.

    • Saliva production decreases with low capillary blood pressure and high blood osmolarity.

    • Short-term satiety lasts for 30-45 minutes post-ingestion; longer-term regulation occurs with reduced blood osmolarity.

  • Water Output Disorders: Include:

    • Volume Depletion: Losing equal amounts of water and Na⁺, as seen in blood loss or chronic vomiting.

    • Dehydration: Occurs from water loss exceeding sodium loss.

    • Fluid Volume Excess: Retention of both water and Na⁺ (e.g., renal failure).

    • Water Intoxication: Retention of excess water relative to sodium, worsening symptoms if plain water replaces lost fluids.

Electrolyte Balance

  • Importance: Critical for physiological functions, including:

    • Metabolism participation as chemically reactive entities.

    • Determining electrical potential across cell membranes.

Major Electrolytes

  • Cations: Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), Magnesium (Mg²⁺), Hydrogen (H⁺).

  • Anions: Chloride (Cl⁻), Bicarbonate (HCO₃⁻), Phosphate (PO₄³⁻).

  • Homeostatic Regulation:

    • Sodium (Na⁺): Functions include nerve impulse transmission, muscular contraction, and overall body water distribution. Typical dietary intake is 3-7 g, while the adult requirement is approximately 0.5 g/day. Key hormones include aldosterone for sodium conservation and natriuretic peptides to inhibit sodium retention.

Potassium (K⁺)

  • Functions: The most abundant cation in ICF and critical for resting membrane potential and action potentials in nerve and muscle.

  • Homeostasis Mechanisms: Primarily regulated by aldosterone. The relationship between Na⁺ and K⁺ in renal excretion is inversely proportional.

Calcium (Ca²⁺)

  • Physiological Roles: Involved in muscle contraction, neurotransmitter release, and blood clotting. Regulated by calcitriol (Vitamin D), parathyroid hormone (PTH), and calcitonin.

Other Electrolytes

  • Chloride (Cl⁻): Contributes to osmolarity, essential for forming stomach acid, and regulates pH; homeostasis managed by its attraction to Na⁺.

  • Magnesium (Mg²⁺): Acts as a cofactor; absorption regulated by Vitamin D.

  • Phosphates (PO₄³⁻): Vital for ATP and pH stabilization, continuously filtered and reabsorbed in kidneys.

Acid-Base Balance

  • Importance: Metabolism requires enzyme function, sensitive to pH; normal range is between 7.35 and 7.45.

  • Buffer Definition: A buffer resists changes in pH by converting strong acids/bases to weaker forms.

  • Major Buffer Systems: Three categories: physiological buffers (respiratory and urinary systems) and chemical buffers (bicarbonate, phosphate, protein systems).

Bicarbonate Buffer System

  • Reaction: CO₂ + H₂O ↔ H₂CO₃ ↔ HCO₃⁻ + H⁺

    • Mechanism for pH regulation.

  • Kidney Function: Can excrete bicarbonate or hydrogen ions to modify pH levels.

Pulmonary Effects on pH

  • Increased CO₂ raises H⁺, lowering pH; decreased CO₂ raises pH. Chemoreceptors modulate ventilation rates in response to pH changes.

Effects of pH Imbalance

  • Acidosis: Hyperpolarizes cells, leading to confusion, muscle fatigue, and potential for serious complications.

  • Alkalosis: Increases nerve excitability, contributing to muscle spasms and seizures.

Chapter 25: Digestive System Part 1

Expected Learning Outcomes

  • List functions and major processes of the digestive system; distinction between mechanical and chemical digestion.

  • Identify the subdivisions of the digestive tract and accessory organs; describe the digestive tract wall's layers and their relation to the peritoneum.

  • Overview of the anatomy from the mouth through the esophagus and functions of saliva.

Functions of the Digestive System

  • **Stages of Digestion:

    1. Ingestion:** Intake of food.
      2. Digestion: Mechanical and chemical breakdown into usable forms.
      3. Absorption: Uptake of nutrients into blood/lymph.
      4. Compaction: Water absorption into feces.
      5. Defecation: Elimination of feces.

Mechanisms of Digestion

  • Mechanical Digestion: Physical breakdown via teeth and muscular actions of the stomach and intestines to increase surface area for enzymes.

  • Chemical Digestion: Hydrolysis reactions breaking down carbohydrates, fats, proteins, and nucleic acids into smaller absorbable units.

Digestive System Structure

  • Digestive Tract: A 30-foot long muscular tube from mouth to anus.

    • Components include: Mouth, pharynx, esophagus, stomach, small intestine, large intestine.

  • Accessory Organs: Teeth, tongue, salivary glands, liver, gallbladder, pancreas.

Structure of Digestive Tract Wall

  • Layers:

    • Mucosa: Inner lining with epithelial cells, including muscularis mucosa that creates folds.

    • Submucosa: Dense connective tissue housing blood vessels, lymphatics, nerves.

    • Muscularis externa: Smooth muscle layers for peristalsis.

    • Serosa: Outer connective tissue layer, also part of mesentery.

Enteric Nervous System

  • Nervous network regulating digestive activity through:

    • Submucosal Plexus: Managing secretions and mucosal movement.

    • Myenteric Plexus: Controlling peristalsis and muscle contractions.

Peritoneum

  • Definition: Double-layered serous membrane.

    • Visceral Layer: Covers abdominal organs.

    • Parietal Layer: Lines the abdominal cavity.

  • Mesenteries: Connective tissue sheets stabilizing the stomach and intestines while allowing movement and facilitating blood supply to digestive organs.

Oral Cavity Functions

  • Functions: Food intake, taste, initial digestion, swallowing, and speech.

  • Anatomical Features: Uvula and arches help contain food during processing; stratified squamous epithelium lines the mouth.

Teeth Classification

  • Types: 32 adult teeth (16 in mandible, 16 in maxilla) including incisors, canines, premolars, and molars.

Tooth Structure

  • Parts: Crown, root, neck; dentin, enamel, cement, and gingival sulcus.

  • Health Considerations: Importance of dental hygiene to prevent cavities and periodontal disease.

Salivary Glands

  • Types: Extrinsic glands include parotid, submandibular, and sublingual glands.

  • Saliva Composition: Includes enzymes and electrolytes, about 1 - 1.5 L produced daily.

  • Control of Salivation: Governed by the salivary nuclei in the brain responding to sensory stimuli.

Chapter 25: Digestive System Part 2

Expected Learning Outcomes

  • Describe the gross and microscopic anatomy of organs including the stomach, liver, gallbladder, pancreas, small intestine, and large intestine.

  • State the functions of each cell type within the gastric mucosa.

Gross Anatomy and Function of Stomach

  • Regions: Cardial, fundus, body, and pyloric; main role in food storage and initial digestion.

  • Wall Composition: Mucosa, submucosa, and muscularis externa include additional oblique muscle layer.

Gastric Secretions and Functions

  • Types of Cells: Mucus cells (mucus), chief cells (gastric lipase, pepsinogen), parietal cells (HCl), and enteroendocrine cells (hormones).

  • Stomach Protection Mechanisms: Mucus coat, tight junctions, and epithelial cell turnover ensure resistance to acid and enzymes.

Liver Anatomy and Functions

  • Largest Gland: Bile production, nutrient synthesis, and metabolism regulation.

  • Microscopic Structure: Hepatocytes form the functional units of the liver.

Bile Pathway to Small Intestine

  • Bile flows from hepatic ducts into the common bile duct and combines with the pancreatic duct before entering the duodenum.

Gallbladder Functionality

  • Functions as bile storage, concentrating bile by water absorption, important for fat digestion.

Pancreas Structure and Function

  • Dual Function: Endocrine (insulin/glucagon secretion) and exocrine (digestive enzyme production) gland.

  • Pancreatic Juice: Alkaline secretion, neutralizes stomach acid, facilitates nutrient digestion.

Small Intestine Overview

  • Function: Main site for chemical digestion and nutrient absorption.

  • Structure: Divided into the duodenum, jejunum, and ileum each serving specific functions for digestion.

Nutrient Absorption Mechanisms

  • Carbohydrates: Digested into monosaccharides, primarily through amylase action, with absorption facilitated by sodium transport mechanisms.

  • Proteins: Decomposed into amino acids absorbed via cotransport mechanisms.

  • Lipids: Emulsified by bile, digested by lipases, and absorbed as chylomicrons.

Large Intestine Anatomy

  • Structure: Comprising the colon and rectum, responsible for fecal formation and water/electrolyte absorption.

  • Motility and Absorption: Haustral contractions and mass movement for residue progression toward defecation; role of intestinal flora in health and gas production.