Digestion and Circulation - PDF

The Digestive System Chapter 48  Vertebrate Digestive Systems tubular gastrointestinal tract and accessory organs Mouth and pharynx (คอหอย) – entry Esophagus – delivers food to stomach Stomach – preliminary digestion Small intestine – digestion and absorption Large intestine –...

The Digestive System Chapter 48  Vertebrate Digestive Systems tubular gastrointestinal tract and accessory organs Mouth and pharynx (คอหอย) – entry Esophagus – delivers food to stomach Stomach – preliminary digestion Small intestine – digestion and absorption Large intestine – absorption of water and minerals Cloaca or rectum – expel waste 2 3  Carnivores – pointed teeth that lack flat grinding surfaces Herbivores – large flat teeth suited for grinding cellulose cell walls of plant tissues Humans have carnivore-like teeth in the front and herbivore-like teeth in the back 4  Mouth and Teeth Inside the mouth, the tongue mixes food with saliva – Moistens and lubricates the food – Contains salivary amylase, which initiates the breakdown of starch – Salivation is controlled by the nervous system Tasting, smelling, and even thinking or talking about food stimulate increased salivation 5  Mouth and Teeth Swallowing – Starts as voluntary action Continued under involuntary control – When food is ready to be swallowed, the tongue moves it to the back of the mouth – Soft palate seals off nasal cavity – Elevation of the larynx (voice box) pushes the glottis against the epiglottis Keeps food out of respiratory tract 6 Mouth and Teeth 7  The Esophagus Muscular tube connecting the esophagus to the stomach Actively moves a bolus through peristalsis Swallowing center in brain stimulates successive one-directional waves of contraction 8  The Stomach Saclike portion of tract Convoluted surface allows expansion 3 kinds of secretory cells – Mucus-secreting cells – Parietal cells Secrete HCl – Chief cells Secrete pepsinogen (inactive form of pepsin that digest protein) 9  The Stomach Low pH in the stomach helps denature food proteins – Activates pepsin and keeps it functioning No significant digestion of carbohydrates or fats occurs Absorption of some water (aspirin and alcohol) Mixture of partially digested food and gastric juice is called chyme Leaves the stomach through the pyloric sphincter to enter the small intestine 10  The Small Intestine About 4.5 m long – small diameter Consists of duodenum, jejunum, and ileum Receives – Chyme from stomach – Digestive enzymes and bicarbonate from pancreas – Bile from liver and gallbladder 11  Epithelial wall is covered with villi – Villi are covered by microvilli – Greatly increase surface area 12  The Large Intestine (colon) Much shorter than small intestine, but has larger diameter Small intestine empties directly into the large intestine at a junction where two vestigial structures, cecum and appendix, remain No digestion occurs Function to reabsorb water, remaining electrolytes, and vitamin K Prepare waste for expulsion 13 14  The Large Intestine Many bacteria live and reproduce within the large intestine – to synthesize vitamin K, which is required for blood clotting Feces compacted and passed to rectum Feces exit anus – Smooth muscle sphincter (involuntary) – Striated muscle sphincter (voluntary) 15 Accessory Organs 16  Accessory Organs Pancreas – Pancreatic fluid is secreted into the duodenum through the pancreatic duct – Enzymes Trypsin and chymotrypsin – proteins into smaller polypeptides Pancreatic amylase – polysaccharides into shorter sugars Lipase – fats into free fatty acids and monoglycerides – Bicarbonate neutralizes acidic chyme 17  Accessory Organs Liver – Body’s largest internal organ – Secretes bile Bile pigments (waste products) and bile salts (for emulsification of fats) – Ingested alcohol and other drugs are taken into liver cells and metabolized – Removes toxins, pesticides, and carcinogens, converting them to less toxic forms Gallbladder – Stores and concentrates bile – Arrival of fatty food in the duodenum stimulates the gallbladder to contract, causing bile to be transported into the duodenum 18  Accessory Organ Function Regulation of blood glucose – After a carbohydrate-rich meal Insulin from pancreas stimulates removal of excess blood glucose by liver and skeletal muscles (glycogen) – When blood glucose levels decrease Glycogenolysis – glucagon from pancreas stimulates liver to break down glycogen to release glucose into blood 19 Circulation 20  Gas Exchange One of the major physiological challenges facing all multicellular animals is obtaining sufficient oxygen and disposing of excess carbon dioxide In vertebrates, the gases diffuse into the aqueous layer covering the epithelial cells that line the respiratory organs Diffusion is passive, driven only by the difference in O2 and CO2 concentrations on the two sides of the membranes and their relative solubilities in the plasma membrane 21  Lungs Lungs of mammals are packed with millions of alveoli (sites of gas exchange) Inhaled air passes through the larynx, glottis, and trachea Bifurcates into the right and left bronchi, which enter each lung and further subdivide into bronchioles Alveoli are surrounded by an extensive capillary network 22 Lungs 23  Lung Structure and Function During inhalation, thoracic volume increases through contraction of two muscle sets – Contraction of the external intercostal muscles expands the rib cage – Contraction of the diaphragm expands the volume of thorax and lungs Produces negative pressure which draws air into the lungs 24 25  Lung Structure and Function Neurons are sensitive to blood PCO2 changes A rise in PCO2 causes increased production of carbonic acid (H2CO3), lowering the blood pH Stimulates chemosensitive neurons in blood vessels Send impulses to respiratory control center in the brain to increase rate of breathing 26  Blood Type of connective tissue composed – Fluid matrix called plasma – Formed elements 27  Formed elements Red blood cells (erythrocytes) – Mature mammalian erythrocytes lack nuclei – RBCs of vertebrates contain hemoglobin Pigment that binds and transports oxygen White blood cells (leukocytes) – Larger than erythrocytes and have nuclei – Can migrate out of capillaries into tissue fluid Platelets Cell fragments that pinch off from larger cells in the bone marrow Function in the formation of blood clots 28 Vertebrate Circulatory Systems Mammals, birds, and crocodilians – 4-chambered heart – 2 separate atria and 2 separate ventricles – Right atrium receives deoxygenated blood from the body and delivers it to the right ventricle, which pumps it to the lungs – Left atrium receives oxygenated blood from the lungs and delivers it to the left ventricle, which pumps it to rest of the body 29 30 31  The Cardiac Cycle Valves open and close as the heart goes through the cardiac cycle Ventricles relaxed and filling (diastole) Ventricles contracted and pumping (systole) “Lub-dub” sounds heard with stethoscope – Lub: Atrioventricular (AV) valves closing – Dub: closing of semilunar valves 32  Blood Vessels Arteries and veins are composed of four tissue layers – Walls too thick for exchange of materials across the wall Capillaries are composed of only a single layer of endothelial cells – Allow rapid exchange of gases and metabolites between blood and body cells 33 Blood Vessels 34  Blood Vessels Arteries and arterioles – Larger arteries contain more elastic fibers and thicker smooth muscle layer in their walls than other blood vessels Recoil each time they receive blood from the heart Veins and venules – Thinner layer of smooth muscles than arteries – Skeletal muscle contractions and one-way venous valves helps return blood to heart 35  Blood Vessels Capillaries – Every cell in the body is within 100 micrometers (μm) of a capillary – Although each capillary is very narrow, so many of them exist that the capillaries have the greatest total cross-sectional area of any other type of vessel Slows blood flow to allow for exchange with extracellular fluid 36  Blood Vessels Blood from the body drains into the right atrium – Superior vena cava drains upper body – Inferior vena cava drains lower body Right and left pulmonary arteries deliver oxygen- depleted blood from the right ventricle to the right and left lungs Pulmonary veins return oxygenated blood from the lungs to the left atrium of the heart Aorta and all its branches are systemic arteries carrying oxygen-rich blood from the left ventricle to all parts of the – Coronary arteries supply oxygenated blood to the heart muscle 37  The Cardiac Cycle Arterial blood pressure can be measured with a sphygmomanometer Systolic pressure is the peak pressure at which ventricles are contracting Diastolic pressure is the minimum pressure between heartbeats at which the ventricles are relaxed Blood pressure is written as a ratio of systolic over diastolic pressure 38 39