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hormones are chemical messengers secreted by endocrine glands into the ______ and transported to specific target cells.
Hormones can be: ______, _________, and _______
An example of each is....
steroids, proteins, and tyrosine derivatives
- Steroid: testosterone, estrogen, progesterone, cortisol
- Tyrosine Derivatives: Thyroxine
- Proteins: Insulin and Glucagon
Distinguish between the mode of action of steroid hormones and protein hormones.
Steroids enter the cell directly because they are lipid soluble, or non polar. The receptor is internal, and is located within the cytoplasm. The steroid binds to the receptor. The hormone receptor complex enters the nucleus and triggers the transcription of a gene. This causes production of a certain protein
Steroid --> Receptor (in cytoplasm) ---> Hormone Receptor Complex ---> nucleus --> transcription of a gene
Protein hormones bind to receptors in the membrane. They can't enter the cell because they are polar, water soluble, and very large. This initiates a series of chemical reactions that produce a second messenger inside of the cell which alters some cell function. This is called signal transduction. This can include altering the transcription or expression of the gene or, more often, the activation of an enzyme.
Protein hormone --> Membrane receptor --> chemical reactions in cytoplasm --> second messenger --> change in cell function or transcription
Outline the relationship between the hypothalamus and the pituitary gland.
The posterior pituitary gland is an extension of the hypothalamus. It grows downward toward the mouth during embryonic development. The posterior pituitary stores and secretes hormones (ADH and oxytocin) in synthesized neurosecretory cells of the hypothalamus. The axons of the neurosecretory cells connect the hypothalamus and posterior pituitary. They synthesize hormones and the posterior pituitary stores and then releases the hormones in response to a nervous impulse.
The anterior pituitary gland is connected to the hypothalamus by portal vessels. It synthesizes and secretes at least 6 different hormones. Is it regulated by tropic hormones produced by neurosecretory cells in the hypothalamus. Some cause it to release hormones while others suppress the release of hormones. Tropic hormones (FSH, LH, TSH) travel through the portal vessels.
Explain the control of ADH (vasopressin) secretion by negative feedback.
ADH, or antidiuretic hormone, acts on the kidneys to promote water retention. It decreases urine output by increasing water reabsorption in the collecting duct. Osmoreceptors in the hypothalamus detect high solute concentration in the blood. Neurosecretory cells produce ADH, which is stored in the posterior pituitary. When osmoreceptors in the hypothalamus detect high solute concentration, this triggers ADH release from the posterior pituitary. When osmoreceptors detect normal blood solute levels, the production and secretion of ADH stop. Thus, the secretion of ADH is controlled by negative feedback.
Digestive juices are secreted into the alimentary canal by glands, including _____ glands, ________ glands in the _______ wall, the ________ and the wall of the _______ intestine.
salivary, gastric, stomach, pancreas, small
Explain the structural features of exocrine glands.
The exocrine portion of the pancreas comprises of rings of acinar cells surrounding small branches of the pancreatic duct. The acinar cells secrete pancreatic juice through the pancreatic duct to the duodenum. In order to make these enzymes there would need to be a lot of rough E.R to support ribosomes and Golgi apparatus to process the products and secrete them by vesicles.
Compare the composition of saliva, gastric juice, and pancreatic juice.
- Saliva: contains amylase, which digests polysaccharides
- buffers which neutralize acids,
- anti-bacterial compounds
- Gastric Juices: HCl, pepsin(ogen), mucus, results in a paste called chyme when mixed with food
- Pancreatic Juice: contains many hydrolytic enzymes (ex nucleases, proteases, lipase, amylase), bicarbonate to neutralize acid in chyme
- Both saliva and pancreatic juice contain amylase
- Gastric Juice and Pancreatic juice contain proteases (pepsin and trypsin)
- Saliva pH 7, Gastric Juice pH 2, pancreatic juice (basice: 7.5-8.2)
Outline the role of membrane bound enzymes on the surface of epithelial cells in the small intestine in digestion.
- Enzymes embedded in the cell membrane of epithelial cells hydrolyze many different molecules.
- Dissaccharidases: ex) sucrase cleaves sucrose into glucose and fructose; Dipeptidases; amino peptidases that break small polypetides into single amino acids; nucleotidases which break nucleotides into sugar, phosphate, and nitrogenous base
- Ensure that digestion is completed (polymers converted to monomers) so material can be absorbed
Outline the reasons for cellulose not being digested in the alimentary canal
- The alimentary canal is the digestive tract
- Enzymes that digest starch by hydrolyzing its alpha linkages are unable to hydrolyze the beta linkages of cellulose because of the distinctly different shapes of these two molecules.
Explain why pepsin and trypsin are initially synthesized as inactive precursors and how they are subsequently activated
- They are secreted as inactive precursors so they don't hydrolyze the cells that are secreting them (damage the lining and cause ulcers)
- Pepsinogen is converted to pepsin by HCl (hydrochloric acid) in the lumen of the stomach, and pepsin then converts more pepsinogen
- Trypsinogen is converted to trypsin by enteropeptidase, which is embedded in the membrane of the epithelial cells of the duodenum.
Discuss the role of gastric juice and Helicobacter pylori in the development of stomach ulcers and stomach cancers
- Helicobacter pylori attacks the mucus lining of the stomach causing inflammation
- Gastric juice attacks the stomach tissues
- If damage is severe and long term, ulcers and cancers can occur
Explain the problem of lipid digestion in a hydrophilic medium and the role of bile in overcoming this.
Lipid molecules tend to coalesce and are only accessible to lipase at the lipid-water interface. Bile molecules have a hydophilic end and a hydrophobic end, and thus prevent lipid droplets from coalescing. The maximum surface is exposed to lipases. It is necessary for lipase to be water soluble. Also, an active site much be available for a hydrophobic substrate to bind to the site.
Explain the structural features of an epithelial cell of a villus as seen in electron micrographs.
- Microvilli: small fingerlike projections of the plasma membrane of epithelial cells on the villus; increase surface area for embedded enzymes and absorption of digested food
- Mitochondria are numerous: membrane pumps and pinocytosis require ATP
- Pinocytotic Vesicles: used to take in droplets of nutrient containing fluid
- Tight Junctions: cement cells of epithelium together; prevents leakage of material in the lumen into the rest of the body
Explain the mechanisms used by the ileum to absorb and transport food
- Facilitated diffusion: digested materials move through channels down a concentration gradient (ex: fructose)
- Active transport: membrane pumps move amino acids, glucose, peptides, vitamins against their concentration gradient, using ATP, into cells
- Endocytosis: intake of larger materials/fluid through the use of a vesicle
List the materials that are egested but not digested and absorbed.
- Cellulose: wrong linkages
- Lignin: present in woody materials
- Bile Pigments: waste product from red blook cell breakdown in liver.
- Bacteria feed on and multiply in material in the colon. Intestinal cells shed from the lining
Outline the control of digestive juice secretion by nerves and hormones.
- Saliva from presence of food in mouth
- juice secreted by epithelial lining, specifically pits
- parasympathetic stimulation of the stomach through the vagus nerve increases secretion
- Stretch receptors in the stomach stimulate the release of gastrin , causing peristalsis to increase
- Gastrin also causes secretion of more gastric juice by the stomach
The liver sythesizes ________ and ________
plasma proteins and cholesterol
The liver has a role in __________.
Explain the role of the liver in regulating levels of nutrients in the blood
The liver removes excess nutrients and minerals so that blood concentration, or osmolarity, is normal.
Outline the role of the live in the storage of nutrients
Liver will store sugar as glycogen and store vitamines and minerals, such as A, D, and iron, to use later
Describe the process of erythrocyte and hemoglobin breakdown in the liver.
- Proteins from Red blood cells, especially hemoglobin, are broken down by the phagocytic cells lining the sinusoids down into amino acids. The excess amino acids are further broken down to produce ammonia. The ammonia combines with Carbon Dioxide to form urea.
- Bilirubin is the main bile pigment. It is formed by the breakdown of heme groups. Globin protein amino acids can be recycled.
Explain the liver damage caused by excessive alcohol consumption
Alcohol is a toxin that is removed by the liver. Because it is toxic, it damages the liver cells, leading to scarring of the liver cells. Excess alcohol interferes with normal metabolism of the liver cells. This results in Fatty liver, which occurs when fat is not converted back into glycogen, and accumulation of toxins because it is unable to break them down. The scarring of the liver can lead to cirrhosis.
Outline atherosclerosis and the causes of coronary thrombosis.
Atherosclerosis: Cholesterol and other lipids build up plaque which develops in the inner walls of the arteries, narrowing their diameters. This causes hypertension, which can lead to coronary thrombosis if a clot adheres to the plaque and then breaks loose. Plaque damages endothelium cells that line arteries. Clots can lodge in coronary arteries and can cause oxygen deprivation. This can ultimately lead to a stroke or heart attack
Discuss risk factors that affect incidence of coronary heart disease
Parents who have experienced heart attacks (genetic), age, being male, smoking, obesity, eating to much saturated fat and cholesterol, lack of exercise
Define Partial Pressure
Measure of the concentration of one gas in a mixture of gases, pressure of a particular gas in a mixture.
Explain the oxygen dissociation curves of adult hemoglobin, fetal hemoglobin, and myoglobin
- All exponentially grow because when oxygen binds to one heme group of hemoglobin, it increases the oxygen affinity for the other three heme groups
- Myoglobin has a much higher affinity for oxygen than hemoglobin, so muscles can take up oxygen from the blood and store it
- Fetal hemoglobin has a higher affinity than adult hemoglobin, so Oxygen diffuses into fetal blood supply from the mother's circulation
Describe how Carbon dioxide is carried by the blood.
Carbon dioxide produced by body tissues diffuses into the interstitial fluid and then into blood plasma. Some remains dissolved in the plasma, but the majority diffuses into Red Blood Cells. Some is bound to hemoglobin inside Red Blood Cells, but most is combined with water to form carbonic acid. This reaction is catalyzed by carbonic anhydrase. Carbonic acid dissociates into H+ and bicarbonate (HCO3-). Bicarbonate then diffuses into plasma where it acts as a buffer against changes in pH. Binding of H+ to hemoglobin prevents acidification of the blood. The process is then reversed in the lungs, so CO2 an diffuse out of the blood.
Outline the circulation of blood through liver tissue.
- Oxygen rich blood goes to the liver by the hepatic artery, which branches off of the aorta. The hepatic portal vein from the intestine acts as a bridge between capillary beds and brings nutrient rich but O2 poor blood form the digestive system. The nutrients were absorbed from the intestine. Blood mixes in the sinusoids, which are capillaires but have a phagocytic cell lining and follow a more convoluted path.
- Liver will store sugar as glycogen and store vitamines and minerals for later use
- The liver removes and stores excess vitamins /nutrients from the blood
- Hepatic vein carries deoxygenated blood fom the live back to the heart.
- Hepatic portal vein enteres liver, and leaves liver to the vena cava
Explain the events of the cardiac cycle
- Left and right atria contract at the same time and then ventricles contract at the same time
- atrial and ventricular diastole: relaxed state
- blood enters the right atrium from vena cava, left atrium from pulmunary vein, during diastole
- Atrial systole (contraction) pumps blood into ventricles
- AV valves close
- Ventricular systole: Right ventricle pumps blood to the pulmonary artery , left ventricle pumps blood into aorta
- Semilunar valve closes
Outline the mechanisms that control the heart beat
- Myogenic: heart muscle contracts independent of nervous stimulation
- SA Node: located in right atrium, sets rate and timing at which the heart contracts (pacemaker)
- Heart rate is adjusted by nerve signals from the medulla (brain stem) to the pacemaker. Cardiac nerve speeds up (sympathetic), vagus nerve slows down (parasympathetic)
- Hormones (epinephrine and norepinephrine) elevated temperature and excercise also increase heart rate
- atria contract in unison
- AV node delays signal to ventricles which causes them to contract after atria, and allows atria to completely empty. Bundle of His and Purkinje fibers carry signal from AV node to ventricular walls; ventricular contraction begins at the apex and proceeds upward.
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