Excretory and Digestive Physiology - Anatomy

The mouth is the start of the gastrointestinal tract. It is the site of both mechanical and chemical digestion via chewing, and saliva, respectively. Saliva contains the enzyme amylase that breaks down carbohydrates.

When holding urine, there are two primary sphincters that help control the release of urine. The internal urethral sphincter is composed of smooth muscle, and is therefore not consciously controlled. The external urethral sphincter is composed of skeletal muscle, which means that it can be consciously controlled.

The detrusor muscle is the smooth muscle found in the walls of the bladder. When contracted, this muscle leads to urination. The rectus abdominis is a region of the abdominal wall. When contracted, this muscle can indirectly assist in urination by reducing the volume of the abdominal cavity and pressuring the bladder.

The human kidney has many functions, all of which are important for sustaining life. The kidney controls blood osmolarity by filtering, reabsorbing, and secreting various ions found throughout the body. The kidney controls fluid volume in the body by this same mechanism. Additionally, the kidney produces erythropoietin and renin which stimulate the production of red blood cells and convert angiotensinogen to angiotensin I, respectively.

The renal capsule is the outermost structure of the kidney. It is the fibrous connective tissue kidney structure that directly surrounds the renal cortex, and is surrounded by a layer of adipose tissue that protects the kidney from trauma. The renal pyramids, renal sinus, and renal medulla are located deep within the kidney.

The urine made within the kidney drains out from the renal pelvis and down the ureter to ultimately be stored in the bladder.

A very large loss of from the patient will lead to a drastic decrease in pH. Therefore, all alkalosis disorders can be ruled out. Additionally, because the pH decrease is unrelated to an increase in carbon dioxide, it is not a respiratory issue - leaving only metabolic acidosis as a diagnosis. Cystic fibrosis involves the overproduction of thick mucous, which causes severe respiratory pathology; other systems are affected too, but excess bicarbonate secretion is not associated with this genetic disease.

Obstruction bilaterally in the ureters leads to decreased GFR due to increased pressure retrograde from the ureters. Bowman space pressure increases to override the GFR pressure. Bowman space pressure does not favor filtration versus GFR pressure (favors filtration).

Serum osmolality is best estimated at around

The glomerulus is a capillary structure associated with the first section of the nephron where blood enters the renal corpuscle. The glomerulus is responsible for filtering fluid, plasma, and dissolved particulates out of circulation and into Bowman's capsule, resulting in a primary filtrate that will go through the rest of the nephron.

The nephron is composed of multiple sections, which are used to alter the solute composition and concentration of the filtrate. The first section is the proximal convoluted tubule. While the solute composition of the filtrate will change due to reabsorption and secretion of specific solutes, the overall concentration does not change. In the proximal convoluted tubule, filtrate is kept isotonic with blood.

The distal convoluted tubule follows the loop of Henle in the nephron structure. In addition to lowering the filtrate concentration, it is also used to reabsorb sodium ions and secrete potassium ions. Aldosterone acts on the distal tubule and further stimulates these two actions.

The collecting duct of a nephron is normally impermeable to water. In the presence of antidiuretic hormone (ADH), aquaporin proteins are inserted, making the collecting duct permeable to water. Water then diffuses into the medulla due to the solute concentration of the surrounding tissues, generated from ion reabsorption in the loop of Henle. This loss of water from the urine makes it more concentrated.

All of the answer choices are true. The macula densa cells are sensitive to changes in concentration of sodium chloride. A decrease in concentration of is detected, which stimulates the macula densa cells to secrete paracrine factors that ultimately increase the pressure in the glomerulus, and thus the glomerular filtration rate, and stimulates the release of renin, which ultimately increases blood pressure, volume and cardiac output.

After filtration of the blood through the glomerulus, approximately 70% of the water and salts is reabsorbed in the proximal convoluted tubule. Additionally, 100% of the glucose is reabsorbed here in a healthy, functioning nephron. The lumenal cells of the proximal convoluted tubule are lined with microvilli and are called brush border cells. Histology of the proximal convoluted tubule is indicative of these structures and the proximal convoluted tubule's lumen can be seen as "crowded" with epithelial surface area, which is distinct from the lumen of the distal convoluted tubule.

ADH acts upon the collecting ducts and distal convoluted tubules of nephrons to increase water reabsorption. It causes an increase in the number of aquaporins in order to allow for this.

The efferent arteriole carries blood away from the glomerulus, and so if it is constricted, the blood pressure behind it will increase. The raise in blood pressure will result in an increase in hydrostatic pressure, pushing additional fluid through the glomerulus i.e elevated glomerular filtration rate. While high hydrostatic pressure does cause damage to the nephron, the nephron rupturing is too extreme of a statement and requires assumptions that are not necessarily valid.

As filtrate passes through the Loop of Henle, the level of concentration of the fluid that will become urine is determined by the length of the loop of Henle (how far into the medulla it dips) and, the osmolality of the medulla. Depending on the levels of circulating hormones, the distal convoluted tubule and collecting duct could be the part of the nephron that determines the concentration of the urine, but to a lesser extent than the length of the loop of Henle.

The descending limb of the loop of Henle is both water permeable and solute impermeable. These properties of the limb allow the filtrate moving through the nephron to become either concentrated or diluted depending on the circumstance.

The afferent and efferent arterioles are located near the glomerulus and control the glomerular filtration rate by constriction and dilation. The peritubular capillaries wind around the proximal convoluted tubule and the distal convoluted tubule to allow for reabsorption and secretion there. The vasa recta on the other hand wind around the loop of Henle and maintain countercurrent multiplication.

The vasa recta wind around the loop of Henle and maintain a countercurrent multiplication to prevent any disregulation or washout of the concentration gradient that has been set up in the renal medulla. Without this gradient, the nephron would be unable to concentrate filtrate. Since the vasa recta carry venous blood, it's oxygen concentration is low and thus needs to go through the pulmonary circuit to pick up more oxygen.