Human Physiology: Digestion, Respiration, Endocrine Systems
Human Physiology: Digestive System
Many nutrients we ingest are large molecules (starch, fats, proteins) that must be broken into smaller molecules (glucose, fatty acids, amino acids) to enter the bloodstream and be transported to cells. This process is called digestion. Vitamins, water, glucose, and minerals are small enough to be absorbed directly without digestion, as is ethanol.
Digestive Organs
The digestive system includes: mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus.
Mouth: Initial Digestion
Two digestive processes occur in the mouth: chewing (mechanical) by teeth and tongue, and insalivation (chemical) by salivary glands. Chewing reduces food to smaller pieces. Insalivation mixes food with saliva, which contains ptyalin (salivary amylase), an enzyme that converts starch (polysaccharide) into maltose (disaccharide).
Esophagus: Passage Tube
After swallowing, the bolus passes through the esophagus via involuntary peristaltic movements of smooth muscles.
Stomach: Temporary Storage
The stomach, with cardia and pylorus valves, stores food, mixes it with gastric juice, and propels it to the small intestine.
Small Intestine: Final Enzymatic Reactions
The food mass moves to the small intestine (duodenum, jejunum, ileum), where digestion completes with pancreatic juice, liver bile, and intestinal enzymes.
Duodenum
Undigested food components are acted upon by pancreatic enzymes and liver bile in the duodenum. Food particles become a nutritional liquid. Bile, stored in the gallbladder, emulsifies fats. Pancreatic juice contains digestive enzymes and bicarbonate to neutralize chyme acidity.
Absorption in the Small Intestine
Digested molecules are absorbed into the bloodstream. Factors aiding absorption include: slightly alkaline pH, bile salts, enzymes, and microvilli.
Large Intestine: End of Digestion
The large intestine includes the cecum (with the appendix), colon, and rectum.
Liver: Metabolic Powerhouse
The liver, the largest gland, stores nutrients, detoxifies, and metabolizes substances in hepatocytes. Functions include: glycogen storage, ammonia conversion, and vitamin storage.
Circulation: Blood Transport
Blood Vessels: Transport Tubes
Blood is transported through arteries, veins, and capillaries.
Arteries: Blood from the Heart
Arteries have thick, elastic walls and carry blood from the heart to tissues.
Veins: Blood to the Heart
Veins have low pressure and valves to prevent backflow.
Capillaries: Final Branching
Capillaries allow substance exchange between blood and tissues.
Heart: Blood Pumping
The heart pumps blood via cardiac muscle contractions (systole) and relaxation (diastole). Coronary circulation supplies the heart with nutrients and oxygen.
Blood Pressure
Blood pressure is the force exerted by blood on artery walls.
Blood Path: Double Circulation
Blood passes twice through the heart: pulmonary (lungs) and systemic (body) circulation.
Pulmonary Circulation
Venous blood (rich in CO2) goes from the right atrium to the right ventricle, then to the lungs via pulmonary arteries.
Systemic Circulation
Oxygenated blood from the left atrium passes to the left ventricle and is distributed throughout the body.
Respiration: Gas Exchange
Airway: Airstream
1. Nose: Nasal cavities filter, heat, and humidify air.
2. Pharynx: Common channel for digestive and respiratory systems.
3. Larynx: Prevents food entry into airways, allows air passage, and voice production.
4. Trachea and Bronchi: Air passes through the trachea to the bronchi.
5. Bronchioles and Alveoli: Bronchi branch into bronchioles and alveoli.
6. Hematosis: Gas exchange in alveoli, where CO2 is replaced with O2.
7. Lungs: Main respiratory organs, surrounded by pleura.
Respiratory Mechanics: Lung Ventilation
Inspiration: Diaphragm and intercostal muscles contract, expanding the rib cage and reducing internal pressure, drawing air in.
Expiration: Muscles relax, increasing internal pressure, forcing air out.
Transport of Respiratory Gases
Oxygen: Transported via plasma and hemoglobin (oxyhemoglobin).
Carbon Dioxide: Transported dissolved in plasma.
Carbon Monoxide (CO): Toxic, binds to hemoglobin, blocking oxygen transport.
Control of Respiratory Movements
Controlled by the respiratory center in the medulla.
Endocrine System: Hormonal Control
The endocrine system, with the nervous system, coordinates body functions via hormones released into the bloodstream.
Target Organs
Organs with hormone receptors.
Hormone Secretion Control: Feedback
Feedback can be positive or negative. Negative feedback is more common, maintaining hormone balance.
Endocrine Glands
Organs secreting hormones into the bloodstream: pituitary, thyroid, parathyroid, adrenal glands, and pancreas.
Pituitary Gland (Hypophysis)
Produces various hormones, controlled by the hypothalamus.
Thyroid Gland
Secretes T3, T4, and calcitonin.
Thyroid Disorders
Hypothyroidism: Decreased T3 and T4 production.
Hyperthyroidism: Increased T3 and T4 production, causing goiter.
Parathyroid Glands
Regulate blood calcium levels.
Adrenal Glands
Consist of cortex and medulla, producing various hormones.
Pancreas
Secretes pancreatic juice and hormones (insulin, glucagon) for blood glucose control.
Insulin
Facilitates glucose uptake by cells.
Glucagon
Stimulates glycogen breakdown into glucose.