Chapter 5 - Structure and Function of Systems PDF

5 – Structure and Function of Systems 5.1 Integumentary System DERMAL LAYERS Stratified squamous epithelial cells Cells in the deepest epidermis are constantly dividing and being pushed Epidermis to...

5 – Structure and Function of Systems 5.1 Integumentary System DERMAL LAYERS Stratified squamous epithelial cells Cells in the deepest epidermis are constantly dividing and being pushed Epidermis toward the surface Dead cells leave behind keratin/phospholipids which waterproof the skin -composed of loose connective tissue Dermis -contains blood vessels, nerve endings and exocrine glands Hypodermis -contains adipose tissue for insulation FUNCTIONS 1. Prevent Water Loss Important for homeostasis / osmoregulation Heat Retention Heat Removal Vasoconstriction (cutaneous) Vasodilation (cutaneous) 2. Thermoregulation Hairs/arrector pilimotor muscles Sweat (osmoregulation) Adipose tissue (hypodermis) From pathogens 3. Physical Protection Fingernails / toenails (made of keratin) protect fingers / toes Callus build up protects areas more prone to abrasion Control Cutaneous vasculature is innervated by the sympathetic branch of the ANS Epinephrine results in cutaneous vasoconstriction and sweating ChadsPrep.com 82 5.2 Skeletal System STRUCTURE/FUNCTION OF SKELETAL SYSTEM 1. Structural Rigidity and Support 2. Calcium Storage Functions 3. Physical Protection 4. Hematopoiesis – red bone marrow synthesizes RBCs, WBCs, and platelets Axial Skeleton Appendicular Skeleton head and trunk All appendages Skeletal skull (including pelvis and shoulder girdle) Structure spinal column sternum ribcage Flat Bones Ex. pelvis, sternum, skull Protect vital organs Spongy bone surrounded by layer of compact bone Contain red marrow (hematopoiesis) Long Bones Bone Arms and legs Types Provide support and mobility Epiphyses contain spongy bone (red marrow - hematopoiesis) surrounded by a layer of compact bone. Epiphyses are coated with articular cartilage. Diaphysis (central shaft) is a tube of compact bone with yellow marrow and blood vessels inside. Epiphyseal plate is the site of bone growth in children / adolescents. ChadsPrep.com 83  JOINTS Synarthrosis Don’t allow movement (ex. Skull) Amphiarthrosis Allow limited movement (ex. intervertebral disks) Freely movable joint 1. Gliding – carpals of the wrist Diarthrosis 2. Hinge – elbow (Synovial) 3. Saddle - thumb 4. Ball and Socket – shoulders and hips Arthritis – Inflammation of a joint (can lead to destruction of the articular cartilage) BONE STRUCTURE Extracellular tissue composed of a calcium phosphate (hydroxyapatite) / collagen matrix Produced by osteoblasts from calcified cartilage Vascular and innervated The osteon is the fundamental unit of compact bone. Osteocyte – mature osteoblast trapped in lacunae in between layers of lamellae in the osteon Osteoclast – cells responsible for reabsorbing Ca2+ from bones CARTILAGE Extracellular tissue secreted by chondroblasts/chondrocytes Composed of a collagen/elastin matrix with proteoglycans interspersed Avascular and not innervated Strong, flexible Hyaline Ex. nose, ears, trachea, ribs, synovial joints (articular cartilage) Strong, rigid Fibro Ex. intervertebral disks Strong, flexible Elastic Ex. ear lobes, epiglottis, larynx LIGAMENTS AND TENDONS Ligaments connective tissue connecting bone to bone Tendons connective tissue connecting muscle to bone HORMONAL REGULATION OF BONE GROWTH / REMODELING Calcitriol (D3) Parathyroid Hormone (PTH) Calcitonin Increases plasma [Ca2+] Increases plasma [Ca2+] Decreases plasma [Ca2+] Secreted by the kidneys Secreted by the parathyroid Secreted by the thyroid Stimulates osteoclasts Stimulates osteoclasts Inhibits osteoclasts Increases renal reabsorption Increases renal reabsorption Increases renal secretion Increases intestinal absorption Increases calcitriol ChadsPrep.com 84 5.3 Muscular System FUNCTIONS OF THE MUSCULAR SYSTEM 1. Support and Mobility 2. Peripheral Circulatory Assistance 3. Thermoregulation (Shivering Reflex) Simultaneous stimulation of antagonistic pairs of skeletal muscles by the SNS MUSCLE TYPES STRIATED (SKELETAL) CARDIAC SMOOTH Striated (sarcomeres) Striated (sarcomeres) Not striated (no sarcomeres) Voluntary Involuntary Involuntary Skeletal system Heart Hollow organs, tubes, sphincters Multi-nucleated Uni-nucleated Uni-nucleated No gap junctions Gap junctions Gap junctions Somatic motor neurons Autorhythmic cells Autonomic efferent neurons Regulated by Ca2+ (SR) Regulated by Ca2+ (SR) Regulated by Ca2+ (extracellular/SR) Troponin / tropomyosin Troponin / tropomyosin calmodulin / MLCK Fastest contractions Intermediate contractions Slowest contractions Muscle Structure and Control of Muscle Contraction t-tubules – branched network of tubules that are continuous with the sarcolemma Allows faster transmission of action potentials from cell surface to the interior of the fiber The sarcoplasmic reticulum stores/sequesters Ca2+ needed for muscle contraction. Red muscle cells (a.k.a. dark meat) contain abundant mitochondria and myoglobin. MUSCLE CELL VOCABULARY muscle fiber = muscle cell sarcolemma = cell membrane sarcoplasm = cytoplasm sarcoplasmic reticulum (SR) = modified ER ChadsPrep.com 85 Regulation of Cardiac Muscle Contraction An action potential (AP) is first produced by autorhythmic cells in the SA node (SinoAtrial node). Contractions aren’t initiated by the nervous system! There is a delay in the transmission at the AV node. The trasmission is spread throughout the atria and ventricles via gap junctions. Nervous System Control Neurons may innervate many muscle fibers. Muscle fibers are innervated by one neuron. Acetylcholine is the neurotransmitter at neuromuscular junctions. Increased muscle tension is accomplished by: 1. Increased recruitment of motor units 2. Increased frequency of stimulation ENERGY CONSUMPTION AND OXYGEN DEBT Active skeletal muscles have a huge demand for ATP. Creatine phosphate can quickly replenish some ATP. Muscles store glycogen for rapid utilization of glucose. AEROBIC RESPIRATION ANAEROBIC RESPIRATION (Lactic Acid Fermentation) Produces lots of ATP Produces ATP quickly Requires lots of O2 Common when aerobic respiration is too slow Myoglobin stores O2 in muscle cells. Common with insufficient O2 for aerobic respiration Lactate must be shuttled to the liver to be converted back to pyruvate (Cori Cycle). ChadsPrep.com 86 Sliding Filament Theory Thin (actin) and thick (myosin) filaments slide past each other during contraction. Action of Myosin 1. Binding of ATP Myosin releases actin. 2. ATP hydrolysis Myosin reattaches to actin (forms crossbridge closer to the center of the sarcomere) 3. Pi is released (Power Stroke) Myosin pulls actin toward the center of the sarcomere 4. ADP is released Myosin is now tightly bound to actin (rigor) Muscle Contraction Contraction 1. Acetylcholine (Ach) is released by a somatic motor neuron. 2. Ach binds Ach receptors/Na+ channels on the muscle fiber (influx of Na+). 3. Depolarization above threshold opens voltage-gated Na+ channels initiating an AP. 4. Voltage-gated Ca2+ channels open in the sarcoplasmic reticulum (outflux of Ca2+). 5. Ca2+ binds to troponin (which is bound to tropomyosin). 6. Troponin removes tropomyosin off of the myosin-binding sites of actin. 7. The myosin powerstroke ensues. Relaxation 8. Ca2+ is actively pumped back into the sarcoplasmic reticulum. 9. Troponin releases Ca2+. 10. Tropomyosin binds to the myosin-binding sites of actin. ChadsPrep.com 87 5.4 Circulatory System FUNCTIONS OF THE CIRCULATORY SYSTEM Circulation to Cells Removal of Metabolic Waste Distributes O2 (from lungs) CO2 (to lungs) Immune cells, antibodies Nutrients, Ions, H2O Ammonia/Urea and H2O Clotting factors (from intestines/liver) (to the kidneys) Hormones Heat (to skin--thermoregulation) Four-Chambered Heart AV Valves – tricuspid and bicuspid (a.k.a. mitral valve) Semilunar Valves – pulmonary valve, aortic valve DIASTOLE SYSTOLE 1. Atria contract 1. Ventricles contract 2. Ventricles fill from atria 2. AV valves close (“lub”) 3. Semilunar valves open 4. Blood flows into aorta / pulmonary artery 5. Semilunar valves close (“dub”) ChadsPrep.com 88 Blood Vessels The entire circulatory system (including the heart) is lined (inner lining) in endothelial cells. ARTERIES VEINS carry blood away from the heart carry blood toward the heart high pressure very low pressure pressure reservoir volume reservoir elastic and lined with smooth muscle larger veins are lined with some smooth muscle no valves valves prevent backflow Arterioles Site of most peripheral resistance Regulate blood flow to individual tissues (variable resistance) Regulated locally to match metabolic needs (by paracrines) Regulated by ANS (sympathetic) and hormones Capillaries Very narrow blood vessels; wide enough for a single RBC to pass through Site of gas/nutrient/waste exchange Site of significant peripheral resistance Portal Circulation Circulation between capillary beds Hypophyseal Portal System – hypothalamus to pituitary gland Hepatic Portal System – from small intestine to liver Renal Portal System – from glomerulus to peritubular capillaries Flow Characteristics Pressure decreases over distance Resistance is greater in smaller vessels CO = Cardiac Output R = Resistance Hypertension can be caused by increased CO, increased peripheral resistance, or increased blood volume. Baroreceptors in the aorta and carotid arteries sense blood pressure – send sensory input to medulla. ChadsPrep.com 89 Capillary Exchange O2 and CO2 can diffuse across the cell membrane. Capillaries are thin (one cell thick) and porous. Nutrients, WBCs, pathogens, and water can pass through the pores (bulk flow). Arteriolar End Hydrostatic > Oncotic High hydrostatic pressure High tissue osmolarity Water is forced out Venular End Oncotic > Hydrostatic Lower hydrostatic pressure Increased blood osmolarity Water is forced back in BLOOD COMPOSITION Plasma Mostly water Contains proteins, ions, dissolved O2 and CO2 Volume regulated by kidneys Erythrocytes (RBCs) Hematocrit – percentage of RBCs in blood Produced in the bone marrow Aged RBCs filtered by spleen No nucleus (short-lived) Contain lots of hemoglobin Transport O2 to tissues; CO2 to lungs Leukocytes (WBCs) Mediators of the immune system Clotting Factors Platelets produced in the bone marrow Fibrinogen/clotting proteins made in liver ChadsPrep.com 90 Mechanism of Clotting/Coagulation 1. Vasoconstriction (paracrine-induced) 2. Tissue damage attracts platelets (forms platelet plug) 3. Tissue damage sets off a coagulation cascade End result is conversion of fibrinogen to fibrin Clot is composed mostly of platelets and fibrin Oxygen Transport by the Blood Hemoglobin can bind up to four O2 molecules Binding is cooperative (sigmoidal binding curve). Hemoglobin vs. myoglobin Bohr Effect - H+ and CO2 decrease the affinity of hemoglobin for O2 CO2 + H2O  H2CO3  H+ + HCO3- CO2 Transport in Blood 1. CO2(aq) 2. CO2 + H2O  H2CO3  H+ + HCO3- 3. Bound to Hemoglobin CONTROL OF THE CIRCULATORY SYSTEM Heart Vascular Smooth Muscle ANS via the medulla Paracrines -- regulated locally to match (both sympathetic and parasympathetic) metabolic needs Hormones ANS (sympathetic) Hormones (epinephrine, ADH, ANF, etc.) ChadsPrep.com 91 5.5 Lymphatic/Immune System FUNCTIONS OF THE LYMPH SYSTEM 1. Recirculation of Plasma Plasma lost from the capillaries is returned to the circulatory system. Lymph is emptied into the venous circulation via the thoracic duct. Fluid flow is unidirectional as lymph vessels contain valves (just like veins). 2. Filter/Destroy Pathogens Lymph nodes serve as reservoirs for macrophages and lymphocytes. Pathogens are often first encountered by the immune system in the lymph nodes. The spleen also acts as a reservoir for macrophages. 3. Absorption of Larger Glycerides Larger glycerides are absorbed directly into the lymph system from the small intestine. They enter the circulatory system via the thoracic duct. ChadsPrep.com 92 Immune System IMMUNE SYSTEM INNATE IMMUNITY ADAPTIVE IMMUNITY Nonspecific Specific Faster response Slower response Inflammatory response Humoral Cell-Mediated Complement system Antibody-mediated Contact-dependent Receptor-mediated IMMUNE SYSTEM CELLS INNATE IMMUNE CELLS ADAPTIVE IMMUNE CELLS Macrophages (phagocytes) T lymphocytes (T cells) Neutrophils (phagocytes) B lymphocytes (B cells) FUNCTIONS OF IMMUNE SYSTEM TISSUES TISSUE FUNCTIONS Bone Marrow Hematopoietic stem cells produce all leukocytes (WBCs) Filters/destroys pathogens Spleen Reservoir of monocytes (immature macrophages) Thymus T cell maturation (including removal of self-antigen recognizing T cells) Lymph Nodes Filters/destroys pathogens; reservoir of macrophages and lymphocytes Innate Immunity Phagocytes ingest foreign material (macrophages and neutrophils) Tears and saliva contain lysozyme; stomach pH ~ 2 Epithelial tissues form a barrier (skin, lining of GI tract and respiratory tract) Complement system – system of proteins effecting lysis of pathogens or virus-infected cells Inflammatory Response Attracts immune cells Promotes tissue repair Mediated through cytokines Natural Killer (NK) Cells Recognize virus-infected cells and induce apoptosis ChadsPrep.com 93 Humoral Immunity Humoral immunity is mediated by antibodies (immunoglobulins) and B cells. Antibodies are expressed on the surface of B cells (B cell receptors). Antibody binding tags an antigen for phagocytosis and activates the complement system. Variable (VDJ) recombination produces antibodies for any antigen. B-Cells B cells are produced in the bone marrow. B cells recognizing self-antigens are eliminated in the bone marrow (clonal deletion). B cells are Antigen Presenting Cells and can activate Th cells (Cell-Mediated Immunity). Primary Humoral Response 1st exposure to a pathogen Takes 5-7 days Mechanism 1. Antigen recognition activates a naive B cell 2. Naive B cell proliferates (clonal selection) 3. Memory cells and plasma cells are produced 4. Plasma cells secrete antibodies Secondary Humoral Response 2nd exposure to a pathogen Memory cell response is much faster ChadsPrep.com 94 Cell-Mediated Immunity Cell-mediated immunity is mediated by Helper T cells and Cytotoxic T cells. T cells are produced in the bone marrow. T cells recognizing self-antigens are eliminated in the thymus (clonal deletion). T cells only recognize antigens presented with MHC (Major Histocompatibility Complex). Helper T Cells (Th) CD4+ (recognize MHC II-bound antigen) Presentation by APC (macrophage, B cell, dendritic cell) Secrete cytokines activating immune cells Cytotoxic T cells (Tc) CD8+ (recognize MHC I-bound antigen) Presentation by any nucleated cell Induce apoptosis of tumor or virus-infected cells ChadsPrep.com 95 5.6 Digestive System Ingestion Mastication breaks up food into smaller pieces. Saliva lubricates food and contains enzymes. Amylase converts starch to disaccharides. Lipase breaks down fats (minimal). Lysozyme is anti-bacterial. The epiglottis prevents food/liquids from entering the trachea. The esophagus is lined in smooth muscle which propels food to the stomach (peristalsis). FUNCTIONS OF THE STOMACH 1. Storage/Churning of Food Stored until the small intestine has room (regulated by the pyloric sphincter) The pyloric sphincter is controlled by the enteric nervous system. The pyloric sphincter also closes in response to cholecystokinin (from the duodenum). Gastric smooth muscle churns (mixes) food aiding in digestion. 2. Partial Digestion a. Partial acid hydrolysis of proteins and carbohydrates (pH ~ 2) HCl is secreted by parietal cells. The stomach is lined in mucus to prevent self-digestion. b. Pepsin functions in proteolysis. Produced/secreted as a zymogen (pepsinogen) by gastric chief cells. Converted to active form by acid-catalyzed proteolysis in the stomach c. Gastric lipase is involved in a small amount of lipid catabolism. Regulation Gastrin secreted by G cells stimulates secretion of HCl and pepsinogen. Histamine stimulates secretion of HCl. Somatostatin inhibits HCl and gastrin secretion. Stimulated by the parasympathetic nervous system; inhibited by the sympathetic) Also regulated by the enteric nervous system ChadsPrep.com 96  FUNCTIONS OF THE LIVER 1. Production of Bile (from cholesterol) Bile aids in digestion of lipids (emulsification) and absorption of fat- soluble vitamins. Bile is stored in the gall bladder. Bile is delivered to the duodenum via the common bile duct. Bile is reabsorbed in the ileum. 2. Regulation of Blood Glucose Insulin stimulates glycogen synthesis (lowers blood sugar). Glucagon, epinephrine, and cortisol stimulate glycogenolysis & gluconeogenesis (raises blood sugar). Cori Cycle - Lactate produced in muscles is converted back into pyruvate and ultimately glucose. 3. Detoxification Drugs/toxins are converted to less harmful substances. 4. Lipid Metabolism Production of lipoproteins (from chylomicrons) Lipoproteins carry cholesterol/triglycerides to the tissues. 5. Production of Plasma Proteins Albumin, fibrinogen, other clotting factors 6. Various other functions FUNCTIONS OF THE PANCREAS 1. Production/Transport of Enzymes amylase – converts polysaccharides to disaccharides lipase – converts triglycerides to fatty acids and monoglycerides nucleases – hydrolyze nucleic acids protease zymogens – inactive precursors activated by proteolysis trypsinogen – activated by enterokinase (and trypsin) in the duodenum chymotrypsinogen –activated by trypsin in the duodenum procarboxypeptidase – activated by enterokinase in the duodenum Enzyme secretion stimulated by cholecystokinin Transported to the duodenum via the pancreatic duct 2. Secretion of Bicarbonate (Exocrine) Keeps the pH in duodenum slightly basic Secretion stimulated by secretin (from the duodenum) Delivered to the duodenum via the pancreatic duct 3. Produces Hormones (Endocrine) Hormones are produced by cells in regions called Islets of Langerhans. a. Glucagon is secreted by  cells (raises blood sugar). Stimulates glycogenolysis / gluconeogenesis by the liver Stimulates release of fats into the blood stream by adipocytes b. Insulin is secreted by  cells (lowers blood sugar). Stimulates glycogen synthesis by liver and skeletal muscle Stimulates glucose uptake by skeletal muscle and adipose tissue c. Somatostatin is secreted by  cells. Inhibits digestion (overall) Inhibits HCl secretion by parietal cells Inhibits secretion of gastrin, histamine, secretin, and cholecystokinin Inhibits glucagon and insulin secretion ChadsPrep.com 97 Small Intestine Duodenum – site of most digestion and absorption Jejunum / Ileum –site of specialized absorption Brush Border Cells – microvilli-covered regions of the lumen of the small intestine FUNCTIONS OF THE SMALL INTESTINE 1. Absorption of Food and Water Carbohydrates - Monosaccharides enter epithelial cells via symport with Na+ (2 active transport). They exit epithelial cells via facilitated diffusion and are taken up by the capillaries. Proteins - Amino acids enter epithelial cells via symport with Na+ (2 active transport). They exit epithelial cells via facilitated diffusion and are taken up by the capillaries. Fats - Fatty acids and monoglycerides diffuse into epithelial cells. They’re converted back into triglycerides and packaged into chylomicrons. Chylomicrons exit epithelial cells into lacteals of the lymphatic system. The lymphatic system empties into the venous circulation at the thoracic duct. 2. Production of Enzymes Enterokinase – Converts trypsinogen to trypsin Trypsin activates other proteases Brush Border Enzymes – Responsible for final digestion of disaccharides and peptides 3. Digestion Carbohydrates - Pancreatic amylase converts polysaccharides into disaccharides. Brush border enzymes convert disaccharides into monosaccharides. Proteins - Pancreatic proteases convert peptides to di- and tri-peptides. Brush border proteases convert di- and tripeptides to amino acids. Fats - Bile emulsifies fat droplets into smaller micelles. Lipases convert triglycerides to fatty acids and monoglycerides. 4. Neutralization of Stomach Acid Bicarbonate from the pancreas neutralizes HCl (pH ~ 8). 5. Hormone Secretion (Endocrine) Cholecystokinin (CCK) – Secreted due to the presence of fatty acids and amino acids Causes the pancreas to release digestive enzymes Causes the gall bladder to release bile secretin – secreted due to presence of acid and causes pancreas to release bicarbonate into the duodenum ChadsPrep.com 98  FUNCTIONS OF THE LARGE INTESTINE 1. Absorption of water, electrolytes, and vitamins There are hundreds of species of bacteria in the colon. They most notably produce vitamin K and biotin (vitamin B7). They also produce GAS. 2. Formation of Feces (compaction) 3. Storage of Feces in the Rectum Regulation Muscular Control – The GI tract is lined in smooth muscle. Peristalsis – contraction of smooth muscle behind the bolus/chime; relaxation ahead Controlled by the autonomic and enteric nervous systems The autonomic and enteric nervous systems also regulate some of the GI secretions. Endocrine Control – The presence of chime causes the release of GI hormones. Paracrines (like histamine) are also involved in local regulation. ChadsPrep.com 99 5.7 Respiratory System FUNCTIONS OF THE RESPIRATORY SYSTEM 1. Gas Exchange Exchange of O2 / CO2 by the alveoli 2. Thermoregulation A significant amount of heat is lost to expired air. 3. Protection from Pathogens and Particulates Nose hairs and mucus contain immunoglobulins. Goblet cells secrete the mucus. Cilia propel mucus toward the pharynx. Macrophages in the alveoli phagocytose pathogens & particulates. 4. pH Regulation Removal of CO2 reduces acidity. Hyperventilation vs. hypoventilation Structure 1. Conducting System mouth/nose → nasal cavity → pharynx → larynx → trachea → primary bronchi → bronchi → bronchioles Warms the air to prevent core heat loss Humidifies air to keep alveoli from drying out Removes pathogens / particulates 2. Exchange Surface Alveoli Bronchioles 3. Muscles/Bones of the Thoracic Cavity Diaphragm Abdominal muscles Intercostals Rib cage ChadsPrep.com 100 Alveolar Structure Thin-walled, air-filled sacs with a huge surface area that are surrounded by capillaries Coated in surfactant (protein phospholipid mixture) which reduces surface tension Type I alveolar cells – make up 95% of alveolar walls and are the site of gas exchange Type II alveolar cells – secrete surfactant Gas exchange results from diffusion due to differential partial pressures (Henry’s Law). Ventilation Inspiration is caused by contraction of the diaphragm and expansion of the rib cage. (The diaphragm is a skeletal muscle.) The lungs are surrounded to two pleural sacs (inner/outer) separated by a thin layer of fluid. The outer pleural sac is connected to the diaphragm and walls of the thoracic cavity. Expansion of the lungs lowers the pressure inside them (Boyle’s Law). Expiration is usually passive elastic recoil of the lungs (resiliency). Due to relaxation of diaphragm and intercostals (rib cage) and alveolar surface tension Forced expiration involves contraction of the abdominal and internal intercostal muscles Control The diaphragm is innervated by the Somatic Nervous System (like all skeletal muscle). Inspiration can be both voluntary and involuntary (controlled by the medulla). Result in Increased Ventilation High plasma [CO2] Low plasma [O2] Low plasma pH REGULATION OF BRONCHIOLE RESISTANCE Bronchoconstriction Bronchodilation Parasympathetic NS Expired CO2 levels Histamine Epinephrine Leukotrienes (inflammation) ChadsPrep.com 101 5.8 Urinary System FUNCTIONS OF THE URINARY SYSTEM 1. Regulation of Blood Pressure (and extracellular fluid volume) Integrated with the cardiovascular system 2. Osmoregulation and Maintenance of Ion Balance 3. Acid-base Balance (either HCO3- or H+ can be excreted) Homeostasis Integrated with the respiratory system 4. Removal of Soluble Nitrogenous Waste (including urea and uric acid) 5. Regulation of Red Blood Cell Synthesis (secretion of erythropoietin) Urination is controlled by the internal and external urethral sphincter muscles Internal urethral sphincter – smooth muscle controlled by the autonomic nervous system External urethral sphincter – skeletal muscle controlled by the somatic nervous system Urine Formation 1. Filtration – Hydrostatic pressure forces plasma from the capillaries of the glomerulus into the lumen of Bowman’s Capsule of the nephrons. 2. Reabsorption – Much of the filtrate is recovered from the nephron tubule into the peritubular capillaries. H2O, ions, glucose, amino acids, proteins, and urea are reabsorbed. 3. Secretion – Certain solutes are concentrated in the urine from the peritubular capillaries K+, H+, and organic molecules (including drugs/toxins) are added to the filtrate. ChadsPrep.com 102 Glomerular Filtration Rate (GFR) is regulated by afferent (primarily) and efferent arterioles. Proximal Tubule – The site of most reabsorption Loop of Henle – Responsible for dilute urine A countercurrent multiplier The descending limb is permeable to water, but impermeable to ions. The ascending limb is impermeable to water. Ions are actively transported out. Distal Nephron (distal tubule and collecting duct) – the site of most secretion Responsible for concentrated urine ChadsPrep.com 103  HORMONAL REGULATION HORMONE EFFECT CAUSE FOR RELEASE ADH Increases water reabsorption by distal nephron Low blood volume (vasopressin) High blood osmolarity Increases Na reabsorption by the distal nephron + Low blood pressure Aldosterone Increases K+ secretion by the distal nephron High [K+] Increased water retention and thirst Increases Na+ and water excretion High blood volume ANF + (decreases Na reabsorption by collecting duct) Vasodilation ChadsPrep.com 104 5.9 Nervous System Nervous System High level control and integration of body systems Adaptive capability to external influences Central Nervous System Includes the brain and spinal cord Controls and integrates body systems Brain Stem Medulla (oblongata) – controls some involuntary functions including blood pressure, breathing, vomiting, and swallowing Pons – relay center between the cerebellum and cerebrum Midbrain – relay center for visual and auditory impulses Cerebellum Integration/coordination of movement Diencephalon Thalamus - integrating/relay center Hypothalamus – homeostasis Influences the endocrine system Influences the autonomic nervous system Pituitary gland Pineal gland Cerebral Cortex (Cerebrum) Site of higher brain functions Divided into two hemispheres connected by corpus callosum Right hemisphere controls motor functions for left side and vice versa ChadsPrep.com 105 Peripheral Nervous System Includes all neurons outside the brain and spinal chord Includes the Somatic and Autonomic Nervous System Neurons are typically either afferent or efferent. Somatic Nervous System Voluntary control of skeletal muscles Somatic motor neurons Have long axon to effector Use acetylcholine as their neurotransmitter Have cell bodies in the spinal cord or brain Somatic sensory neurons Have long dendrite to cell body Have cell bodies in the dorsal root ganglion Have axon that extends to spinal cord or brain stem Autonomic Nervous System Involuntary control of: SYMPATHETIC PARASYMPATHETIC 1. Smooth muscle “fight or flight” “rest and digest” 2. Cardiac muscle Increase energy availability Store energy 3. Endocrine/exocrine glands Activated by stress Important for maintaining homeostasis Antagonistic control between sympathetic and parasympathetic branches There are two neurons in series connecting the CNS to effector. A postganglionic neuron has its cell body in an autonomic ganglion. Integration with the Endocrine System The hypothalamus coordinates control of both the autonomic nervous system and the endocrine system to maintain homeostasis. The hypothalamus specifically regulates the pituitary gland (endocrine system) and the medulla (ANS). Examples of Feedback Control If body temperature drops, the sympathetic PNS causes vasoconstriction of the blood vessels to the skin. If body temperature rises, the sympathetic nervous system activates sweating. ChadsPrep.com 106 Neuron Cell body (soma) – contains nucleus and most organelles and controls metabolic activity and biosynthesis Axon – transmits impulses away from the cell body Dendrite – receives signals and transmits it toward the cell body Myelin Sheath – insulating sheath around axons Made by glial cells (Schwann cells in the PNS and oligodendrocytes in the CNS) Glial Cells (a.k.a. neuroglia) – non-neuronal cells that provide support/protection to neurons Nodes of Ranvier – gaps in myelin sheath (faster impulse propagation with saltatory conduction) Synapse – site of impulse propagation between cells (via neurotransmitters) Synaptic Transmission Presynaptic Neuron 1. An action potential reaches the synaptic knobs 2. Voltage-gated Ca2+ channels open 3. Uptake of Ca2+ 4. Exocytosis of neurotransmitter Postsynaptic Cell 5. Neurotransmitter binds receptors 6. Ion channels open 7. Polarization is increased or decreased 8. Neurotransmitter activity is terminated Diffuses away, degraded, or re-uptake EPSP – Excitatory postsynaptic potential IPSP – Inhibitory postsynaptic potential Neurotransmitter binding can be excitatory (EPSP) or inhibitory (IPSP). The additive effect of EPSPs and IPSPs at all synapses determines whether an action potential is generated (summation). Synaptic Fatigue – inhibition under constant or persistent stimulus; caused by depletion of synaptic vesicles Neurotransmitters include acetylcholine, norepinephrine, epinephrine, serotonin, dopamine, GABA, a few amino acids and even a couple gases ChadsPrep.com 107 Action Potentials Resting Potential of a neuron is ~-70mV Na+/K+ pump (active transport) and K+ leak channels maintain resting potential 1. Depolarization (must exceed threshold of -50mV) 2. Voltage-gated Na+ channels open (further depolarization) 3. Voltage-gated Na+ channels close 4. Voltage-gated K+ channels open (repolarization/hyperpolarization) 5. Voltage-gated K+ channels close 6. Resting potential restored by Na+/K+ pump Refractory Period - Voltage-gated Na+ channels are inactivated until the resting potential is re-established Propagation of Action Potentials Saltatory Conduction – Depolarization ‘jumps’ to each successive node of Ranvier speeding up transmission All or Nothing Principle – Strength of an action potential never varies Intensity of a stimulus is related to the frequency of firing ChadsPrep.com 108 5.10 Endocrine System Nervous System vs. Endocrine System Nervous System – effects are fast-acting but short-lasting Endocrine System – effects aren’t as fast-acting but are longer lasting Endocrine vs. Exocrine Endocrine Glands – ductless glands that release hormones into the bloodstream that bind specific receptors on/in their target cells Exocrine Glands – glands that release their products via ducts either into the GI tract or outside the body Hormone – a chemical messenger secreted into the blood for transport to a target(s) TYPES OF HORMONES AMINO ACID-DERIVED Catecholamines T3 and T4 PEPTIDE STEROID (Epinephrine, Norepinephrine) Water Hydrophilic Hydrophobic Hydrophilic Hydrophobic Solubility Synthesis Rough ER Smooth ER Adrenal Medulla Thyroid Transport in Carrier Protein- Carrier Protein- Free in plasma Free in plasma Blood bound bound Cytoplasmic or Target Nuclear Cell Membrane Nuclear Cell Membrane Receptor Receptor Receptor Transcription Transcription Mechanism 2nd messenger 2nd messenger Regulation Regulation Fast Acting / Slow Acting / Half-Life Short Long Short-lived Long-lasting The only amino-acid derived hormones to note are epinephrine, norepinephrine, T3, and T4. The sex hormones and all hormones from the adrenal cortex are steroids. Androgens (testosterone), estrogens and progesterone, cortisol and aldosterone All remaining hormones are peptides (most hormones in general are peptides). Mechanisms of Hormone Action Enzyme Regulation Transcriptional Regulation Regulating solute transport across membranes Hormone Regulation Nervous System – hypothalamus controls anterior and posterior pituitary gland Tropic Hormones – hormones that control other hormones Hypothalamus controls anterior pituitary via tropic hormones Anterior pituitary controls gonads, adrenal cortex, and thyroid via tropic hormones Endocrine Gland itself acts as a sensor -cells sense blood glucose levels and release insulin when they are above threshold ChadsPrep.com 109 Regulation of the Endocrine System ANTERIOR PITUITARY POSTERIOR PITUITARY FSH (gonads) Oxytocin (mammary glands, uterus) LH (gonads) ADH (kidneys) ACTH (adrenal cortex) GH (generic) Prolactin (mammary glands) ChadsPrep.com 110  GLAND HORMONE TARGET FUNCTION Hypothalamus tropic hormones anterior pituitary modify release of anterior pituitary hormones FSH (follicle stimulating hormone) ovaries/testes follicle development / spermatogenesis LH (luteinizing hormone) ovaries/testes ovulation / testosterone synthesis ACTH (adrenocorticotropic hormone) adrenal cortex increase cortisol release Anterior Pituitary TSH (thyroid stimulating hormone) thyroid increase thyroid hormone synthesis GH (growth hormone) bone, muscle growth prolactin mammary glands milk production ADH (antidiuretic hormone/vasopressin) kidneys/blood vessels water reabsorption/ vasoconstriction Posterior Pituitary oxytocin mammary glands / uterus milk release / contraction T4 (thyroxin) generic increase metabolism Thyroid T3 (triiodothyronine) generic increase metabolism calcitonin bone lower blood Ca2+ Parathyroid PTH (parathyroid hormone) bone increase blood Ca2+ Thymus thymosin thymus T cell development (childhood) Heart ANF (atrial natriuretic factor; aka ANP) kidneys vasodilation / increases Na+ excretion (lowers blood pressure) glucagon (−cells) liver, muscles, adipose increase blood glucose Pancreas insulin (β-cells) liver, muscles, adipose decrease blood glucose somatostatin (-cells) stomach, duodenum inhibit digestion pancreas inhibit glucagon and insulin secretion Duodenum Cholecystokinin (CCK) Pancreas, gall bladder Secretion of digestive enzymes, bile; satiety epinephrine heart, blood vessels, liver fight or flight Adrenal Medulla norepinephrine heart, blood vessels, liver fight or flight cortisol (glucocorticoids) generic long-term stress response Adrenal Cortex aldosterone (mineralocorticoids) kidneys reabsorption of Na+; excretion of K+ (increases blood pressure) erythropoietin bone marrow increase RBC synthesis Kidneys calcitriol bone increase blood Ca2+ Testes testosterone testes / generic spermatogenesis, secondary sex characteristics estrogen uterus / generic menstrual cycle, secondary sex characteristics Ovaries progesterone uterus menstrual cycle, pregnancy ChadsPrep.com 111 5.11 Reproductive System GAMETOGENESIS FEMALE MALE Gonads ovaries testes Germ Cells oogonia spermatogonia Gametes ova (ovum) spermatozoa Products 1 ovum, 2 polar bodies 4 spermatozoa Timing puberty → ~50 years old puberty → death Oogenesis 1. Oogonia develop into primary oocytes prenatally (arrested in prophase I) 2. Follicle maturation A primary oocyte splits into a secondary oocyte and first polar body concluding meiosis I Meiosis is arrested in metaphase II 3. Ovulation 4. Fertilization Meiosis II is only completed after fertilization ChadsPrep.com 112 Spermatogenesis Spermatozoa are produced in the seminiferous tubules of the testes Sustentacular cells regulate sperm development (provide “sustenance”) Leydig Cells (Interstitial Cells) secrete testosterone Maturation occurs as spermatogonia migrate towards the lumen of the seminiferous tubules Maturation continues in the epididymis but is completed in the female reproductive tract Sperm are much smaller than the ovum. Sperm contribute genetic material only (its nucleus). The ovum contributes genetic material, organelles, and cytoplasm. ChadsPrep.com 113 Male Reproductive System MALE REPRODUCTIVE ORGANS Testes Produce sperm (seminiferous tubules) GONADS Secrete testosterone (Leydig cells) EXTERNAL Penis Urethra allows passage of urine and sperm GENITALIA Scrotum External sac allowing temperature regulation of testes INTERNAL Accessory glands Contribute secretions to semen GENITALIA ducts ChadsPrep.com 114 Female Reproductive System FEMALE REPRODUCTIVE ORGANS Ovaries Produce ova GONADS Secrete estrogen and progesterone EXTERNAL Labia majora/minora Protect internal genitalia GENITALIA clitoris Vagina Receptacle for penis; birth canal INTERNAL Uterus Womb GENITALIA Fallopian Tubes Transport ova from ovary to the uterus Uterus – Endometrium – layer of glandular epithelium shed during menstruation Myometrium – thick layer of smooth muscle Cervix – opening of the uterus -dilated slightly during fertile days and greatly during childbirth ChadsPrep.com 115 Female Reproductive Cycle OVARIAN CYCLE PHASE DAYS EVENTS Follicular 1-13 FSH stimulates follicle maturation Phase FSH and LH stimulate production of estrogen by the maturing follicle Ovulation 14 A spike in LH results in release of a secondary oocyte The follicular remains become the corpus luteum Luteal Phase 15-28 The corpus luteum secretes estrogen and progesterone The corpus luteum degenerates throughout the phase due to low levels of LH Estrogen/progesterone levels drop at the end of this phase signaling menstruation Pregnancy If fertilization/implantation occurs, the placenta produces human chorionic gonadotropin (hCG). hCG keeps the corpus luteum from degenerating in place of LH. The corpus luteum maintains high levels of estrogen and progesterone (first 2-3 months). The placenta then takes over production of estrogen and progesterone for the remainder of pregnancy. The endometrium isn’t shed and ovulation doesn’t occur during pregnancy (LH remains low). Negative Feedback LH/FSH inhibit GnRH Estrogen inhibits GnRH, LH, FSH Inhibin (from follicle) inhibits FSH ChadsPrep.com 116  MENSTRUAL CYCLE PHASE DAYS EVENTS Menses 1-7 Endometrium is shed (signalled by low levels of progesterone) Proliferative Phase 7-14 Endometrial growth (due to increasing levels of estrogen) Secondary Phase 15-28 Endometrial cells accumulate nutrients ChadsPrep.com 117 Parturition Typically occurs between weeks 38 and 40 Exact trigger(s) for the induction of labor are not known 1. Cervix softens and dilates / pelvic ligaments loosen (days leading up to labor) 2. Baby “drops” and pushes on the cervix 3. Cervical stretch triggers the release of oxytocin by the posterior pituitary gland 4. Oxytocin induces contractions 5. Contractions → stretching → contractions → stretching (positive feedback cycle) 6. Baby exits birth canal Lactation Prolactin stimulates milk production Estrogen and progesterone stimulate development of breasts / mammary glands but inhibit prolactin Estrogen and progesterone levels fall after delivery Prolactin levels increase ~10-fold Suckling stimulates the release of prolactin and oxytocin (needed for milk release) ChadsPrep.com 118