Body Structure and Function Final Review PDF

Body Structure and Function Final Review  Nerve Tissue Nerve Cells are neurons, or nerve fibers Made of cell body – which contains the nucleus, dendrites, and axons Neurons are found in the central nervous system or close to it in the trunk of the body. ...

Body Structure and Function Final Review  Nerve Tissue Nerve Cells are neurons, or nerve fibers Made of cell body – which contains the nucleus, dendrites, and axons Neurons are found in the central nervous system or close to it in the trunk of the body.  Nerve Tissue Dendrites are processes that transmit impulses toward the cell body. The one axon of a neuron transmits impulses away from the cell body.  Types of Neurons Sensory neurons (afferent neurons) carry impulses from receptors to the CNS. Motor Neurons (efferent neurons) carry impulses from CNS to effectors. Interneuron – a nerve cell entirely within the CNS. Some are concerned with thinking, learning, and memory.  Nerve Tissue The axons and dendrites are wrapped in specialized cells called Schwann cells. These layers are the myelin sheath, which electrically insulates neurons from one another.  Synapses The neurotransmitter diffuses across the synapse, combines with specific receptor sites on the cell membrane of the postsynaptic neuron This is carried by the next neuron’s axon to the next synapse and so on… A chemical inactivator at the cell body or dendrite of the postsynaptic neuron quickly inactivates the neurotransmitter. This prevents unwanted continuous impulses  Synapses Ensure 1 way transmission of impulses Neurotransmitter is acetylcholine, which is in the CNS, and in much of the PNS. Cholinesterase is the inactivator of acetylcholine.  Spinal Cord Transmits impulses to and from the brain and is the integrating center for the spinal cord reflexes. Enclosed in the vertebral canal and the meninges, the spinal cord is well protected from mechanical injury. Extends from the foramen magnum of the occipital bone to the disc between the first and second lumbar vertebrae.  Spinal Cord Ascending tracts carry sensory impulses to the brain. Descending tracts carry motor impulses away from the brain. Central Canal contains cerebrospinal fluid and is continuous with cavities in the brain called ventricles  Spinal Cord Reflexes Involuntary response to a stimulus, that is, an automatic action stimulated by a specific change of some kind. Spinal Cord Reflexes are those that do not depend directly on the brain, although the brain may inhibit or enhance them.  Reflex Arc Pathway nerve impulses travel when a reflex is elicited, and there are five essential parts: Receptors-detect a change and generate impulses Sensory neurons-transmit impulses from receptors to the CNS Central Nervous System – contains 1 or more synapes Motor Neurons – transmit impulses from the CNS to the effector Effector – performs its characteristic action.  The Brain Medulla – extends from the spinal cord to the pons and is anterior to the cerebellum. Cardiac centers, vasomotor centers, and respiratory centers; cough, sneezing, swallowing, and vomiting centers.  Pons – bulges anteriorly from the upper part of the medulla. 2 respiratory centers that work with those in the medulla to produce a normal breathing rhythm.  Thalamus – superior to the hypothalamus and inferior to the cerebrum. Concerned with sensation. The thalamus integrates the impulses, or puts them together so the cerebrum feels the whole and is able to interpret the sensation quickly  The Brain Cerebellum-separated from the medulla and pons by the fourth ventricle and is inferior to the occipital lobes of the cerebrum. All the functions are concerned with movement, including coordination, regulation of muscle tone, the appropriate trajectory and endpoint of movements, and the maintenance of posture and equalibrium. All involuntary, therefore, below the level of consciousness.  The Brain Hypothalamus-located superior to the pituitary gland and inferior to the thalamus. Functions of the Hypothalamus: – Production of antidiuretic hormone (ADH) and oxytocin – Production of releasing hormones that stimulate the secretion of hormones by the anterior pituitary gland.  Hypothalamus Functions Regulation of body temperature by promoting responses such as sweating in a warm environment or shivering in a cold environment Regulation of food intake Integration of the functioning of the autonomic nervous system, which in turn regulates the activity of organs such as the heart, blood vessels, and intestines.  Hypothalamus Functions Stimulation of visceral responses during emotional situations. Regulation of body rhythms, such as secretion of hormones, sleep cycles, changes in mood or mental alertness.  The Brain Cerebrum- largest part of the brain. Two hemispheres separated by the longitudinal fissure. At the base of the fissure is the corpus callosum, a band of 200 million neurons that connects the right and left hemispheres. Within each hemisphere is a lateral ventricle.  Frontal Lobes Motor areas generate impulses for voluntary movement. Largest portion for the movement of the hands and face for precise movements. Left motor area controls movement on right side of the body, and the right motor area controls movement on the left side of the body.  Frontal Lobes Anterior to the motor areas are the premotor areas, which are concerned with learned motor skills that require a sequence of movements. (shoe tying) Broca’s motor speech area, which controls the movements of the mouth involved in speaking.  Parietal Lobes General sensory areas receive impulses from receptors in skin and feel and interpret the cutaneous sensations. Left area for right side of body and visa versa Receive impulses from stretch receptors in muscles for conscious muscle sense The largest portions are for sensation in hands and face Taste areas, overlap with temporal lobes, receive impulses from taste buds on the tongue elsewhere in oral cavity  Temporal Lobes Olfactory areas receive impulses from receptors in the nasal cavities for the sense of smell. Auditory areas receive impulses from receptors in the inner ear for hearing. Speech areas concerned with thought that precedes speech  Occipital Lobes Impulses from the retinas of the eyes travel along the optic nerves to the visual areas in the occipital lobes. Spatial relationships; judging distance and seeing in three dimensions.  Association Areas These areas give us our personality, a sense of humor, and the ability to reason and use logic. Learning and memory are also functions of these areas. Hippocampus is responsible for our memory  Basal Ganglia Paired masses of gray matter within the white matter of the cerebral hemispheres. Functions are subconscious aspects of voluntary movement, and they work with the cerebellum. Regulate muscle tone, and coordinate accessory movements such as swinging of the arms when walking or gesturing while speaking.  Corpus Callosum Band of nerve fibers that connects the left and right cerebral hemispheres. This band of nerve fibers lets the hemispheres communicate with each other.  Meninges and Cerebrospinal Fluid Connective tissue membranes that cover the brain and spinal cord are the meninges Dura Mater is the thick outermost layer, which lines the skull and vertebral canal Arachnoid membrane is the middle membrane made of web like strands of connective tissue Pia Mater is the innermost very thin membrane on the surface of the spinal cord and brain. Between the arachnoid and pia mater is the subarachnoid space, which contains cerebrospinal fluid  Choroid Plexus Choroid plexus is a capillary network that forms cerebrospinal fluid from blood plasma. It is a continuous process, and the CSF then circulates in and around the CNS Some CSF must be reabsorbed. This is done by the arachnoid villi into the blood in cranial venous sinuses. This becomes blood plasma again.  Blood Types ABO group – a person with Type A blood has the A antigen on the blood cells. This says I belong to this person. Also, each person has antibodies for all the blood types they are not. If the wrong blood is given, the cells will clump and then rupture causing kidney damage and renal failure. Blood Types: A, B, AB, O  Cross and typing ensures the correct blood is given. O is the universal donor because they don’t have the a or b antigens. AB is the universal recipient because they have the antigens for both A and B  RH Factor Rh antigen are Rh positive. If Rh negative receives Rh-positive blood by mistake, antibodies will be formed. A first mistaken transfusion often doesn’t cause problems, because antibody production is slow. A second transfusion, will bring about a transfusion reaction, with hemolysis and kidney damage.  Mediastinum and Pericardial Membranes Mediastinum Pericardial Membranes – Fibrous Pericardium – Parietal Pericardium – Visceral Pericardium – Serous Fluid  Chambers-Vessels and Valves 4 chamber of heart made of cardiac muscle called myocardium. Lined with endocardium; smooth for prevention of clotting Upper chambers are atria, separated by interatrial septum Lower chambers are ventricles, separated by interventricular septum  Know the pathway of blood through the heart. Inferior/superior vena cava through aorta. Systemic circulation  Atrial Natriuretic Hormone Atria produce ANH. When the walls of the atria are stretched by increased blood volume or blood pressure, ANH is released. ANH decreases the reabsorption of sodium ions by the kidneys. Water follows. This decreases blood volume and blood pressure.  Left Ventricle Walls are thicker than right ventricle for more forceful contraction. Blood flows from left ventricle through aortic semilunar valve (also have papillae and chordae tendineae) to the body (aorta)  Heart Valves  Coronary Vessels 1st branches of the ascending aorta Branch into smaller arteries, arterioles, and capillaries. The coronary capillaries merge to form coronary veins, which empty blood into a large coronary sinus that returns blood to the right atrium. Purpose is to supply blood to the myocardium.  If obstruction occurs, ischemia is the result (decreased oxygen supply). If blood flow is not restored, it will become an infarct (dead tissue)  Cardiac Cycle Sequence of events in one heartbeat. Simultaneous contraction of the two atria, followed by simultaneous contraction of the two ventricles Systole is the term for contraction. Diastole is the term for relaxation.  Cardiac Conduction Sequence of mechanical events that is regulated by the electrical activity of the myocardium. Heart cells have the ability to contract spontaneously. The heart generates its own beat. Sinoatrial node Atrioventricular node Bundle of His Bundle Branches Purkinje fibers  Arrythmias irregular heartbeats from harmless to life threatening. Palpitations irregular heartbeats from time to time. Fibrillation very rapid and uncoordinated ventricular beat that is ineffective for pumping blood.  Heart Rate 60-80 resting pulse (rate of SA node) 100 tachycardia Well conditioned people have slower heart rates.  Cardiac Output Amount of blood pumped by a ventricle in 1 minute. Stroke volume is the term for the amount of blood pumped by a ventricle per beat. (60-80) Cardiac output: stroke volume x pulse Starling’s Law of the Heart Venous Return Ejection Fraction  Arteries Carry blood from the heart to capillaries Small arteries are arterioles. Outer and middle layers thick. 3 layers of arteries – Tunica intima – Tunica media – Tunica externa  Veins Carry blood from capillaries back to the heart. Smaller veins are venules. Same three layers as arteries but inner layer has valves. These valves prevent backflow. Middle and out layer is thin because bp is low in veins.  Anastomoses Connection or joining, of vessels, artery to artery or vein to vein. Purpose is to provide alternate pathways for the flow of blood if one vessel becomes obstructed. Arterial Venous  Capillaries Carry blood from arterioles to venules. Walls only 1 cell in thickness Blood flow is regulated by precapillary sphincters. Constrict and dilate according to the needs of the tissues. Sinusoids are larger and more permeable than other capillaries. Permit larger substances such as proteins and blood cells to enter or leave the blood.  Sinusoids are found in hemopoietic tissues such as red bone marrow and spleen, liver and pituitary gland.  Exchanges in Capillaries Sites for exchange of materials between the blood and tissue fluid surrounding cells. Gases move by diffusion from their area of greater concentration to the area of lower concentration. BP in arterioles is 30-35 mHg, and the pressure of the surrounding tissue fluid is much lower, about 2 mmHg.  Because capillary blood pressure is higher, the process of filtration occurs, which forces plasma and dissolved nutrients out of the capillaries and into tissue fluid. BP decreases as it reaches the venous end of capillaries.  Albumin contributes to colloid osmotic pressure of blood This is a pulling pressure. At the venous end of capillaries, the presence of albumin in the blood pulls tissue fluid into the capillaries which also brings into the blood the waste products produced by cells.  The tissue fluid that returns to the blood also helps maintain normal blood volume and blood pressure. Excess tissue fluid enters lymph capillaries to be recycled as plasma.  Hepatic Portal Circulation Subdivision of the systemic circulation in which blood from the abdominal digestive organs and spleen circulates through the liver before returning to the heart. Blood from the capillaries of the stomach, small intestine, colon, pancreas, and spleen flows into two large veins, the superior mesenteric vein and the splenic vein, which unite to form the portal vein.  The portal vein takes blood into the liver, where is empties blood into the sinusoids, the capillaries of the liver. From the sinusoids, blood flows into hepatic veins to the inferior vena cava and back to the right atrium. Purpose is to enable the liver to modify the blood from the digestive organs and spleen.  Some nutrients may be stored or changed, bilirubin from the spleen is excreted into bile, and potential poisons are detoxified before the blood returns to the heart and the rest of the body. Detoxify’s alcohol, and if glucose is high, changes it to glycogen to store.  Pulmonary Circulation Right ventricle pumps blood into the pulmonary artery, which divides into the right and left pulmonary arteries, one for each lung. Within the lungs each artery branches extensively into smaller arteries and arterioles, then to capillaries. The pulmonary capillaries surround the alveoli of the lungs.  The alveoli are where the exchanges of oxygen and carbon dioxide take place. The capillaries unite to form venules, which merge into veins, and finally into the two pulmonary veins from each lung that return blood to the left atrium. This oxygenated blood will then travel through the systemic circulation.  Notice that the pulmonary veins contain oxygenated blood; these are the only veins with high oxygen content.  Systemic Circulation Left ventricle pumps blood into the aorta. – Ascending aorta – Aortic arch – Thoracic aorta – Abdominal aorta  The branches of the aorta take the blood into arterioles and capillary networks throughout the body. Capillaries merge to form venules and veins. The veins from the lower body take blood to the inferior vena cava The veins from the upper body take blood to the superior vena cava. These return blood to the right atrium.  Maintenance of Systemic Blood Pressure Venous Return – Skeletal muscle pump – Constriction of the veins – Respiratory pump Heart Rate and Force Peripheral Resistance Elasticity of the large arteries Viscosity of the blood Loss of Blood Hormones Intrinsic Mechanisms of Regulation of BP Heart – Starlings Law Kidneys – – Blood flow – Renin-angiotensin Mechanism  Know Respiratory pathways.  Pharnyx The soft palate is elevated during swallowing to block the nasopharynx and prevent food or saliva from going up rather than down.  Opening into the nasopharynx are 2 eustachian tubes, which extend to the middle ear cavities. The purpose is to permit air to enter or leave the middle ears, allowing the eardrums to vibrate properly. Nasopharynx is a passageway for air only  Oropharynx is behind the mouth. Food and air passageway  Laryngopharynx is a food and air passageway. Opens anteriorly to the larynx and posteriorly into the esophagus. Contraction of the muscular wall of the oropharynx and laryngopharynx is part of the swallowing reflex.  Larynx Called the voice box. Functions are speaking and air passageway between the pharynx and trachea. Made of 9 pieces of cartilage connected by ligaments. This prevents collapse to keep air passages open. Thyroid cartilage is the largest. Epiglottis is the uppermost.  Vocal cords are on either side of the glottis (the opening between them)  Trachea and Bronchial Tree 4-5 inches long extends from the larynx to the primary bronchi. 16-20 C shaped pieces of cartilage, which keep the trachea open. The gaps are posterior, to permit the expansion of the esophagus when food is swallowed. Mucosa is ciliated epithelium with goblet cells. They sweep toward the pharynx.  Right and Left primary bronchi are the branches of the trachea that enter the lungs. Within each lung, each primary bronchus branches into secondary bronchi leading to the lobes of each lung (3 right, 2 left) Further branching is called the bronchial tree. The smaller branches of this tree are the bronchioles. The smallest bronchioles terminate in clusters of alveoli, the air sacs of the lungs.  Serous membranes of the thoracic cavity. – Parietal pleura lines the chest wall – Visceral pleura is on the surface of the lungs. – Between the plural membranes is serous fluid, which prevents friction and keep the two membranes together during breathing.  Alveoli Functional units of the lungs are the air sacs alveoli. Simple squamous epithelium. In the spaces between clusters of alveoli is elastic connective tissue, which is important for exhalation. Macrophages Alveoli is surrounded by a capillary network, which permits efficient diffusion of gases.  Each alveoli is lined with a thin layer of tissue fluid Pulmonary surfactant mixes with the tissue fluid within the alveoli  Mechanism of Breathing Ventilation is the term for the movement of air to and from the alveoli. Inhalation and exhalation are brought about by the nervous system and respiratory muscles. The respiratory centers are located in the medulla and pons. The medulla generates impulses to the respiratory muscles. The stimulus for breathing is high CO2  Respiratory Muscles Diaphragm External intercostal muscles Internal intercostal muscles  Inhalation The diaphragm contracts, moves downward, and expands the chest cavity from top to bottom.  The external intercostal muscles pull the ribs up and out, which expands the chest cavity from side to side and front to back. As the chest cavity is expanded, the parietal pleura expands with it. Intrapleural pressure becomes even more negative as a sort of suction is created between the pleural membranes.  The adhesion created by the serous fluid permits the visceral pleura to be expanded too, and this expands the visceral pleura to be expanded too, and this expands the lungs as well. As the lungs expand, intrapulmonic pressure falls below atmospheric pressure, and air enters the nose and travels through the respiratory passages to the alveoli.  Exhalation Begins when motor impulses from the medulla decrease, and the diaphragm and external intercostal muscles relax. As the chest cavity becomes smaller, the lungs are compressed, and their elastic connective tissue, which was stretched during inhalation, recoils and also compresses the alveoli.  Exchange of Gases External Respiration Internal Respiration Transport of Gases in the Blood Most oxygen is carried in the blood bonded to hemoglobin in RBCs. The mineral iron is part of hemoglobin and gives this protein its oxygen carrying ability.  Pulmonary Volumes Tidal Volume Minute Respiratory Volume Inspiratory Reserve Expiratory Reserve Vital Capacity Residual Air  Acidosis Alkalosis pH  Divisions of the Digestive System Know Digestive pathways Alimentary Tube – Mouth to anus – Digestion takes place within the oral cavity, stomach, and small intestine – Most absorption takes place in the small intestine Accessory Organs – These contribute something to digestion  Types of Digestion Mechanical Digestion – Physical breaking up of food into smaller pieces Chemical Digestion – Complex chemical molecules are changed into much simpler chemicals that the body can utilize. – Enzymes aid the digestion.  Function is chewing. This mechanically breaks food into smaller pieces and mixes it with saliva. Structures of teeth – Root is enclosed in a socket in the mandible and maxillae. – Pulp Cavity Contains blood vessels and nerve endings of the trigeminal nerve. – Enamel Provides a hard chewing surface and is resistant to decay Dentin forms the roots of the teeth  Salivary Glands Digestive secretion in the oral cavity is saliva. Secretion is continuous Mostly water and small amount of digestive enzyme  Pharynx Oropharynx and laryngopharynx are food passageways connecting the oral cavity to the esophagus. No digestion, just mechanical movement of food.  Esophagus Muscular tube that takes food from the pharynx to the stomach. No digestion takes place. Peristalsis propels the food to the stomach even if upside down. Lower esophageal sphincter is the junction of the stomach and esophagus. – Relaxes to permit food to enter the stomach, the contracts to prevent backup of stomach contents.  Structural Layers of the Alimentary Tube Mucosa lining of alimentary tube The epithelium secrete mucus, which lubricates the passage of food, and also secretes the digestive enzymes of the stomach and small intestines. Below the epithelium are lymph nodules that contain lymphocytes to produce antibodies, and macrophages to phagocytize bacteria  Submucosa – Many blood vessels and lymphatic vessels – Meissner’s plexus (millions of nerves fibers)– innervate the mucosa to regulate secretions. – Parasympathetic increase secretions – Sympathetic decrease secretions.  External Muscle Layer Contractions of this muscle layer break up food and mix it with digestive juices. One way contractions of perstalsis move food toward the anus. Auerbach’s plexus is the portion of the enteric nervous system – Sympathetic decrease peristalsis – Parasympathetic increase peristalsis  Serosa Mesentary – Visceral peritoneum, a serous membrane. Peritoneum – Lining the abdominal cavity – One continuous membrane. The serous fluid prevents friction when the organs slide against each other.  Stomach Extends from the esophagus to the small intestine. Reservoir for food, digestion proceed gradually. Mechanical and chemical digestion  Small Intestine Extends from the stomach to the cecum of the large intestine. Duodenum is the first 10 inches. Jejunum – 8 feet long Ileum – 11 feet long  Digestion is completed in the small intestine Mucosa includes cells with microvilli and goblet cells that secrete mucus.  Liver Digestive function is the production of bile. The digestive function of bile is accomplished by bile salts, which emulsify fats in the small intestine. This is mechanical.  Gallbladder Bile in the hepatic duct of the liver flows through the cystic duct into the gallbladder, which stores bile until it is needed in the small intestine. It concentrates bile by absorbing water.  Pancreas Amylase digests starch to maltose. Lipase converts emulsified fats to fatty acids and glycerol. Trypsin digests polypeptides to shorter chains of amino acids.  Produces bicarbonate juice which is alkaline. This neutralizes the gastric juice that enters the duodenum to prevent damage.  Absorption Most absorption takes place in the small intestine by microvilli. This increases the amount of absorption  Liver regulates blood glucose levels, amino acids, store certain vitamins, and remove potential poisons from the blood  Large Intestine Colon, 5 feet in length. Extends from ileum of the small intestine to the anus, the terminal opening. Cecum is the first portion. Ileocecal valve, which is not a sphincter but serves the same purpose, prevention of backflow  Attached to the cecum is the appendix, which is a small dead-end tube with lymphatic tissue. The appendix is removed if it become impacted with stool. Ascending Transverse Descending Sigmoid Colon, turns medially and downward Rectum – 6 inches long Anal canal – last inch  No digestion takes place.  Normal Flora- vitamins absorbed are those produced by this flora; this inhibits pathogens Vitamin K is produced and absorbed also Everything absorbed by the colon is passed through the portal circulation Functions – Absorption of water, minerals, and vitamins and elimination of undigestible material.  Defecation of Feces Consists of cellulose and other undigestible material, dead and living bacteria, and water. Defecation reflex, spinal cord reflex that may be controlled voluntarily.  Other Functions of the Liver Carbohydrate Metabolism Amino Acid Metabolism Lipid Metabolism Synthesis of plasma proteins Formation of bilirubin Phagocytosis Storage Detoxification  Each kidney has an indentation called a hilus on the medial side. The renal artery enters the kidney, and the renal vein and ureter emerge at the hilus. Renal artery is a branch of the abdominal aorta. Renal vein returns blood to the inferior vena cava. Ureter carries urine from the kidney to the bladder.  Renal Corpuscle Consists of a glomerulus surrounded by a Bowman’s capsule. Glomerulus is a capillary network that arises from afferent arterioles and empties into efferent arterioles. Efferent is smaller than afferent to maintain high blood pressure in glomerulus.  Bowman’s capsule is the expanded end of a renal tubule; it encloses the glomerulus. The inner layer is permeable because of podocytes The outer layer is not permeable. The space between the inner and outer layers of Bowman’s capsule contain renal filtrate, the fluid formed from the blood in the glomerulus and will eventually become urine.  Renal Tubule Continues from the Bowman’s capsule and consists of : – Proximal Convoluted Tubule (renal cortex) – Loop of Henle (renal medulla) – Distal convoluted tubule (renal cortex)  The distal convoluted tubules from several nephrons empty into a collecting tubule. Several collecting tubules unite to form a papillary duct that empties urine into a calyx of the renal pelvis. The microvilli in the proximal convoluted tubule provide for efficient exchanges of materials.  All parts of the renal tubule are surrounded by peritubular capillaries, which arise from the efferent arteriole. These capillaries will receive materials reabsorbed by the renal tubules.  Blood Vessels in the Kidney Blood branches from the abdominal aorta to the renal artery. It then branches into smaller arteries. The smallest arteries give rise to afferent arterioles in the renal cortex. From the afferent arterioles, blood flows into the glomeruli, to efferent arterioles, to peritubular capillaries, to veins within the kidney, to the renal vein, and to the inferior vena cava.  2 sets of capillaries where exchanges take place. These will form urine from the blood plasma.  Formation of Urine Glomerular filtration Tubular reabsorption Tubular secretion  Glomerular Filtration Blood pressure forces plasma, dissolved substances, and small proteins out of the glomeruli and into Bowman’s capsules. This fluid is no longer plasma but called renal filtrate. The blood pressure is higher in these capillaries, about 60 mmHg.  The pressure in Bowman’s capsule is very low, and very permeable. 20-25% of blood becomes renal filtrate in Bowman’s capsules. Blood cells and proteins are to large, so they stay in blood. Waste products, nutrients and minerals are also present in renal filtrate.  Glomerular filtration rate (GFR) is the amount of renal filtrate formed by the kidneys in 1 minute, averages 100-125 ml. Altered if rate of blood flow changes. More is more, less is less.  Tubular Reabsorption Takes place from the renal tubules into the peritubular capillaries. In a 24 hour period, the kidneys form 150- 180 liters of filtrate, and normal output in that time is 1-2 liters. 99% is reabsorbed into the blood by the peritubular capillaries.  Most reabsorption and secretion take place in the proximal convoluted tubules, whose cells have microvilli Distal Convoluted tubules and collecting tubules are important for reabsorption.  Mechanisms of Reabsorption Active Transport – cells of the renal tubule use ATP to transport most of the useful materials from filtrate to blood. These include: glucose, amino acids, vitamins, and positive ions. Threshold level Reabsorption of Ca Reabsorption of Na and excretion of K  Passive transport Osmosis Pinocytosis  Tubular Secretion Substances are actively secreted from blood in peritubular capillaries into the filtrate in the renal tubules. Waste products such as ammonia, creatinine, meds, and hydrogen to adjust pH.  Kidney’s Acid-Base Balance If to acidic, kidneys will secrete more Hydrogen into renal filtrate and return more bicarbonate to blood. If to alkaline, kidneys will secrete more bicarbonate to renal filtrate and return more Hydrogen to blood.  Other Functions of Kidneys Secretion of Renin Secretion of Erythropoietin Activation of Vitamin D  Urinary Bladder Reservoir for accumulating urine, and it contracts to eliminate urine.  Mucosa is transitional epithelium, which permits expansion without tearing. When empty they appear wrinkled (rugae) Floor contains a triangular area called trigone, which has no rugae and does not expand. The points of the trigone are the openings of the two ureters and that of the urethra.  Around the opening of the urethra the muscle fibers of the detrusor form the internal urethral sphincter.  Urethra Carries urine from the bladder to the exterior. The external urethral sphincter is made of skeletal muscle and is under voluntary control.  Urination Reflex Urination is also called micturition or voiding. Spinal cord reflex over which voluntary control can be exerted. Stimulus is stretching of the detrusor. Bladder can hold 800 ml urine but the reflex is activated before this point.  When the level reaches 200-400 ml the stretching generates sensory impulses that travel to the spinal cord. Motor impulses return to detrusor causing contraction. At the same time the external urethral sphincter is voluntarily relaxed, urine flows into the urethra, and the bladder is emptied. Voluntary control is not possible beyond a certain point.