Exam 1 Study Guide: Temperature Regulation, Endocrine System, and Digestive System

Temperature Regulation and Metabolism

Homeothermy and Homeostasis

Homeotherms are organisms that maintain a relatively constant internal body temperature regardless of external environmental changes. This process is a key aspect of homeostasis, the body's ability to maintain stable internal conditions.

• Human Body Temperature: The average human body temperature is approximately 37°C (98.6°F).

• Temperature Control: On cold days, the body conserves heat through vasoconstriction and shivering. On hot days, it dissipates heat via vasodilation and sweating.

• Role of the Hypothalamus: The hypothalamus acts as the body's thermostat, detecting changes in blood temperature and initiating appropriate responses to maintain homeostasis.

Metabolism and Energy Production

Metabolism encompasses all chemical reactions in the body, including those that produce and use energy.

• Daily Calorie Requirement: Adult males typically require about 2,500 kcal/day, while adult females require about 2,000 kcal/day. These values vary with age, activity level, and health status.

• ATP Formation: Adenosine triphosphate (ATP) is the primary energy currency of the cell. It is produced by:

  • Aerobic Respiration: Occurs in the presence of oxygen, producing up to 36 ATP per glucose molecule.

  • Anaerobic Respiration: Occurs without oxygen, yielding 2 ATP per glucose and producing lactic acid.

  • Creatine Phosphate System: Provides a rapid source of ATP in muscle cells for short bursts of activity.

Pathologies Related to Temperature Regulation

• Hypothermia: Abnormally low body temperature, which can impair physiological functions.

• Heat Exhaustion: Caused by excessive heat and dehydration, leading to weakness and fainting.

• Heat Stroke: A life-threatening condition where the body's temperature regulation fails, causing dangerously high body temperature.

Endocrine System

General Functions and Definitions

The endocrine system regulates body functions through the secretion of hormones, which are chemical messengers released into the bloodstream.

• Hormone: A chemical messenger produced by endocrine cells that affects target cells.

• Endocrine Gland: Ductless gland that secretes hormones directly into the blood.

• Endocrine Tissue/Cell: Cells or tissues that produce hormones.

• Target Cell: Cell with receptors specific to a particular hormone.

• Autocrine: Hormone acts on the cell that secreted it.

• Paracrine: Hormone acts on neighboring cells.

• Endocrine: Hormone acts on distant target cells via the bloodstream.

• Half-life: Time required for half the hormone to be removed from the blood.

Endocrine vs. Exocrine Glands

• Endocrine Glands: Secrete hormones into the blood (e.g., thyroid, pituitary).

• Exocrine Glands: Secrete substances through ducts to an epithelial surface (e.g., sweat, salivary glands).

Nervous System vs. Endocrine System

• Nervous System: Fast, uses electrical impulses and neurotransmitters, effects are short-lived.

• Endocrine System: Slower, uses hormones, effects are longer-lasting and widespread.

Hormones: Chemical Nature and Modes of Action

• Chemical Nature: Hormones can be peptides, steroids, or amines.

• Modes of Action: Bind to receptors on target cells, triggering intracellular signaling pathways.

Pituitary Gland and Hypothalamus

• Relationship: The hypothalamus controls the pituitary gland via releasing and inhibiting hormones.

• Anatomical Differences: The anterior pituitary is connected to the hypothalamus by blood vessels (hypophyseal portal system), while the posterior pituitary is connected by nerve fibers.

Tropic Hormones

• Definition: Hormones that regulate the function of other endocrine glands.

• Examples: Thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH).

Major Endocrine Glands: Location, Structure, and Hormones

Gland	Location	Main Hormones
Pituitary	Base of brain	GH, TSH, ACTH, FSH, LH, PRL, ADH, Oxytocin
Thyroid	Neck, below larynx	T3, T4, Calcitonin
Parathyroid	Posterior thyroid	PTH
Adrenal Cortex	Above kidneys	Cortisol, Aldosterone
Adrenal Medulla	Above kidneys	Epinephrine, Norepinephrine
Pancreas	Behind stomach	Insulin, Glucagon
Gonads	Ovaries/Testes	Estrogen, Progesterone, Testosterone
Pineal	Brain	Melatonin

Other Chemical Messengers

• Adipose Tissue: Leptin

• Kidney: Erythropoietin, Renin

• Heart: Atrial natriuretic peptide (ANP)

• Intestinal Endocrinocytes: Secretin, Cholecystokinin

• Thymus: Thymosins

Feedback Control

• Negative Feedback: Most hormone regulation (e.g., insulin lowers blood glucose, which reduces insulin secretion).

• Positive Feedback: Rare; e.g., oxytocin during childbirth increases uterine contractions.

Homeostatic Imbalance: Diabetes Mellitus

• Definition: Chronic high blood glucose due to insufficient insulin production or action.

• Regulation of Insulin: Insulin is secreted by pancreatic beta cells in response to high blood glucose, promoting glucose uptake by cells.

Digestive System

Structure and Functions

The digestive system breaks down food into absorbable units and eliminates waste. It consists of the gastrointestinal (GI) tract and accessory organs.

• GI Tract: Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anal canal.

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

Histology of the GI Tract

• Tunics (Layers): Mucosa, submucosa, muscularis externa, serosa/adventitia.

Key Definitions

• Mechanical Digestion: Physical breakdown of food (chewing, churning).

• Chemical Digestion: Enzymatic breakdown of macromolecules.

• Peristalsis: Wave-like muscle contractions moving food along the GI tract.

• Peritoneum: Serous membrane lining the abdominal cavity.

• Mesenteries: Folds of peritoneum supporting the intestines.

• Deglutition: Swallowing.

Oral Cavity and Pharynx

• Oral Cavity: Site of ingestion, mechanical and chemical digestion begins here.

• Pharynx: Divided into nasopharynx, oropharynx, laryngopharynx.

• Deglutition: Soft palate and uvula prevent food from entering the nasal cavity; epiglottis prevents entry into the trachea.

Esophagus and Stomach

• Esophagus: Muscular tube; mucosa is stratified squamous epithelium.

• Stomach: Regions include cardia, fundus, body, pylorus; rugae allow expansion; four tunics; gastric glands contain chief cells (pepsinogen), parietal cells (HCl, intrinsic factor).

Sphincters of the GI Tract

Sphincter	Location	Function
Inferior Esophageal (Cardiac)	Between esophagus and stomach	Prevents reflux
Pyloric	Between stomach and duodenum	Regulates gastric emptying
Ileocecal	Between ileum and cecum	Prevents backflow into small intestine
Anal	End of rectum	Controls defecation

Small Intestine

• Segments: Duodenum (shortest), jejunum, ileum (longest).

• Specializations: Circular folds (plicae circulares), villi, microvilli increase surface area for absorption.

• Duodenal (Brunner) Glands: Secrete alkaline mucus to neutralize stomach acid.

• Intestinal Glands (Crypts of Lieberkühn): Secrete intestinal juice.

• Peyer Patches: Lymphatic nodules in the ileum for immune defense.

• Intrinsic Factor: Secreted by parietal cells; necessary for vitamin B12 absorption in the ileum.

Large Intestine, Rectum, and Anal Canal

• Segments: Cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal.

• Flexures: Hepatic (right colic) and splenic (left colic) flexures.

• Specializations: Muscularis forms teniae coli; haustra are pouches.

• Anal Sphincters: Internal (smooth muscle, autonomic control), external (skeletal muscle, voluntary control).

• Vitamin K Synthesis: Produced by gut bacteria in the large intestine.

Accessory Digestive Organs

• Liver: Four lobes; supported by coronary, falciform, and round ligaments; porta hepatis is the entry/exit for vessels and ducts. Functions include bile production, metabolism, detoxification.

• Gallbladder: Stores and concentrates bile.

• Pancreas: Exocrine (pancreatic acini secrete digestive enzymes), endocrine (islets of Langerhans secrete insulin and glucagon).

Biliary Apparatus

Component	Function
Left/Right Hepatic Ducts	Drain bile from liver lobes
Common Hepatic Duct	Formed by left and right hepatic ducts
Cystic Duct	Connects gallbladder to common bile duct
Common Bile Duct	Delivers bile to duodenum
Main Pancreatic Duct	Delivers pancreatic juice to duodenum
Hepatopancreatic Ampulla (of Vater)	Union of bile and pancreatic ducts
Hepatopancreatic Sphincter (of Oddi)	Controls flow into duodenum
Major Duodenal Papilla	Opening into duodenum

• Path of Bile and Pancreatic Juice: Bile flows from liver → hepatic ducts → common hepatic duct → (joins cystic duct from gallbladder) → common bile duct → hepatopancreatic ampulla → duodenum. Pancreatic juice follows a similar path via the main pancreatic duct.

Regulation of the Digestive System

• Chemical Regulation: Hormones such as gastrin, secretin, and cholecystokinin regulate digestive secretions and motility.

• Nervous System Control: Enteric nervous system and autonomic nervous system modulate digestive activity.

Physiology of Digestion

• Mechanical Digestion: Includes chewing, peristalsis, segmentation, haustral churning, and mass movements.

• Chemical Digestion: Enzymes break down carbohydrates, proteins, and fats into absorbable units in various regions of the GI tract.

• Absorption: Nutrients are absorbed via active and passive transport into blood capillaries or lacteals (for fats).

Digestive Enzymes and Breakdown Products

Macromolecule	Enzyme	Breakdown Product
Carbohydrates	Amylase	Monosaccharides
Proteins	Pepsin, Trypsin	Amino acids
Fats	Lipase	Fatty acids, glycerol

Common Digestive Pathologies

• Peptic Ulcer: Erosion of stomach or duodenal lining.

• Hiatal Hernia: Stomach protrudes through diaphragm.

• Pyloric Stenosis: Narrowing of the pyloric sphincter.

• GERD: Gastroesophageal reflux disease; acid reflux into esophagus.

• Lactose Intolerance: Inability to digest lactose due to lactase deficiency.

• Pancreatic Cancer, Cystic Fibrosis, Gall Stones, Hemorrhoids: Various effects on digestion and absorption.

Focus: Diabetes and Glucose Homeostasis

• Glucose Homeostasis: Maintained by insulin (lowers blood glucose) and glucagon (raises blood glucose).

• Diabetes Mellitus: Results from impaired insulin secretion or action, leading to hyperglycemia.