CH 21: Digestion

Layers and Processes of the Gastrointestinal (GI) Tract

The GI tract is composed of several layers and undergoes complex processes to facilitate digestion and absorption of nutrients.

• Four Layers of the GI Tract: The layers are mucosa, submucosa, muscularis externa, and serosa/adventitia. Each layer has distinct functions in protection, secretion, absorption, and motility.

• Basic Processes in the GI Tract: These include ingestion, propulsion (peristalsis and segmentation), mechanical digestion, chemical digestion, absorption, and defecation.

• Kinds of Fluids Secreted: The GI tract secretes saliva, gastric juice, pancreatic juice, bile, and intestinal juice, each containing enzymes and other substances for digestion.

• Types of Movements: Peristalsis moves food along the tract, while segmentation mixes contents and enhances absorption.

Additional info: The enteric nervous system regulates many GI functions independently of the central nervous system.

Control and Regulation of Digestion

Digestion is regulated by neural and hormonal mechanisms to ensure proper breakdown and absorption of nutrients.

• Enteric Nervous System: Controls local reflexes and coordinates motility and secretion.

• Central Nervous System: Modulates digestive activity via the autonomic nervous system.

• Hormonal Control: Hormones such as gastrin, secretin, and cholecystokinin regulate digestive secretions and motility.

Digestion and Absorption of Nutrients

Different regions of the GI tract are specialized for the digestion and absorption of carbohydrates, proteins, and fats.

• Carbohydrate Digestion: Begins in the mouth with salivary amylase and continues in the small intestine.

• Protein Digestion: Starts in the stomach with pepsin and is completed in the small intestine by pancreatic enzymes.

• Lipid Digestion: Occurs mainly in the small intestine with the help of bile and pancreatic lipase.

• Water and Vitamin Absorption: Water is absorbed throughout the GI tract; vitamins are absorbed in the small intestine (fat-soluble with fats, water-soluble by diffusion or active transport).

Enzymes and Secretions

Digestive enzymes and secretions play a crucial role in breaking down food into absorbable units.

• Enzymes: Amylases, proteases, lipases, and nucleases are secreted by various glands and organs.

• Bile: Produced by the liver, stored in the gallbladder, and released into the small intestine to emulsify fats.

Chapter 22: Metabolism

Appetite Regulation

Appetite is controlled by hormones and neural signals that regulate hunger and satiety.

• Ghrelin: Stimulates hunger; secreted by the stomach.

• Leptin: Promotes satiety; secreted by adipose tissue.

Energy Balance and Metabolic Rate

Energy balance is the relationship between energy intake and expenditure. Metabolic rate is the rate at which the body uses energy.

• Basal Metabolic Rate (BMR): The energy required to maintain basic physiological functions at rest.

• Factors Affecting Metabolic Rate: Age, sex, body composition, activity level, and hormones.

Equation for BMR:

Additional info: Resting metabolic rate is slightly higher than BMR due to minimal activity.

Glycogen and Fat Storage

The body stores energy in the form of glycogen and fat for later use.

• Glycogen: Stored in liver and muscle; provides short-term energy.

• Fat: Stored in adipose tissue; provides long-term energy.

Metabolic Pathways

Metabolism includes catabolism (breakdown) and anabolism (synthesis) of biomolecules.

• Catabolism: Breakdown of molecules to release energy.

• Anabolism: Synthesis of complex molecules from simpler ones.

• Glycogenesis: Formation of glycogen from glucose.

• Glycogenolysis: Breakdown of glycogen to glucose.

• Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources.

• Lipogenesis: Formation of fat from excess nutrients.

Chapter 14: Cardiovascular Physiology

Blood Flow and Pressure

Blood flow is driven by pressure gradients and regulated by vessel resistance and cardiac output.

• Blood Flow: Movement of blood through vessels; depends on pressure and resistance.

• Relationship Between Volume and Pressure: Increased volume increases pressure; pressure drives flow.

• Resistance: Opposition to flow; affected by vessel diameter, length, and blood viscosity.

• Equation for Flow:

• Vasoconstriction: Narrowing of blood vessels; increases resistance and blood pressure.

• Vasodilation: Widening of blood vessels; decreases resistance and blood pressure.

Cardiac Cycle and ECG

The cardiac cycle describes the sequence of events in one heartbeat, and the ECG records the electrical activity of the heart.

• Myocardial Contractile Cells vs. Pacemaker Cells: Contractile cells generate force; pacemaker cells set the rhythm.

• ECG Peaks: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

• Diastole vs. Systole: Diastole is relaxation and filling; systole is contraction and ejection.

Autonomic Regulation of Heart Rate

The autonomic nervous system modulates heart rate and cardiac output.

• Sympathetic Stimulation: Increases heart rate and contractility.

• Parasympathetic Stimulation: Decreases heart rate.

Key Abbreviations

• CO: Cardiac Output

• SV: Stroke Volume

• HR: Heart Rate

• EDV: End-Diastolic Volume

• ESV: End-Systolic Volume

Equation for Cardiac Output:

CH 15: Blood Flow and the Control of Blood Pressure

Types of Blood Vessels and Pressure

Blood vessels vary in structure and function, influencing blood pressure and flow.

• Arteries: Carry blood away from the heart; high pressure.

• Veins: Return blood to the heart; low pressure.

• Capillaries: Site of exchange; thin walls and low pressure.

• Blood Pressure: Systolic (peak during contraction), diastolic (lowest during relaxation), pulse pressure (difference between systolic and diastolic).

Vasoconstriction, Vasodilation, and Angiogenesis

Vasoconstriction and vasodilation regulate vessel diameter and blood flow; angiogenesis is the formation of new blood vessels.

• Vasoconstriction: Increases resistance and blood pressure.

• Vasodilation: Decreases resistance and blood pressure.

• Angiogenesis: Formation of new blood vessels; important in growth and healing.

Regulation of Blood Pressure

Blood pressure is regulated by neural, hormonal, and local mechanisms.

• Baroreceptors: Detect changes in blood pressure and initiate reflexes to maintain homeostasis.

• Local Control: Autoregulation by tissues; endocrine control via hormones like angiotensin II.

• Site of Resistance: Arterioles are the main site of resistance in the vascular system.

Capillary Exchange

Capillaries allow exchange of gases, nutrients, and wastes between blood and tissues.

• Types of Capillaries: Continuous, fenestrated, and sinusoidal; differ in permeability and location.

• Exchange Site: Filtration occurs at the arterial end; absorption at the venous end.

The Lymphatic System

The lymphatic system returns excess fluid to the bloodstream and provides immune functions.

• Functions: Drains interstitial fluid, transports dietary lipids, and facilitates immune responses.

• Lymph Flow: Starts in lymphatic capillaries, moves through vessels and nodes, and returns to venous circulation.

• Edema: Occurs when lymphatic drainage is impaired, leading to fluid accumulation.

Cardiovascular Disease

Cardiovascular diseases are influenced by genetic, lifestyle, and environmental factors.

• Causes: Hypertension, atherosclerosis, obesity, diabetes, smoking, and inactivity.

• Risk Factors: Age, family history, high cholesterol, high blood pressure, and unhealthy diet.

Table: Comparison of Blood Vessel Types

Additional info: Capillary permeability varies by type; continuous capillaries are least permeable, sinusoidal are most.