Principal heart sounds

1. S1: closure of AV valves;typically auscultated as a single sound 

Clinical note: In certain circumstances, S1 may be accentuated. This occurs when the valve leaflets are “slammed” shut in early systole from a greater than normal distance because they have not had time to drift closer together. Three conditions that can result in an accentuated S1 are a shortened PR interval, mild mitral stenosis, and high cardiac-output states or tachycardia.

2. S2: closure of semilunar valves in early diastole , normally “split” during inspiration . S2: best appreciated in the 2nd or 3rd left intercostal space

Clinical note: Paradoxical or “reversed” splitting occurs when S2 splitting occurs with expiration and disappears on inspiration. Moreover, in paradoxical splitting, the pulmonic valve closes before the aortic valve, such that P2 precedes A2. The most common cause is left bundle branch block (LBBB). In LBBB, depolarization of the left ventricle is impaired, resulting in delayed left ventricular contraction and aortic valve closure.

3. S3: ventricular gallop, presence reflects volume-overloaded state 
 
 Clinical note: An S3 is usually caused by volume overload in congestive heart failure. It can also be associated with valvular disease, such as advanced mitral regurgitation, in which the “regurgitated” blood increases the rate of ventricular filling during early diastole.
 
4. S4: atrial gallop, S4: atrial contraction against a stiff ventricle, often heard after an acute myocardial infarction.

Clinical note: An S4 usually indicates decreased ventricular compliance (i.e., the ventricle does not relax as easily), which is commonly associated with ventricular hypertrophy or myocardial ischemia. An S4 is almost always present after an acute myocardial infarction. It is loudest at the apex with the patient in the left lateral decubitus position (lying on their left side).

As the contents of the stomach become thoroughly liquefied, they pass into the duodenum, the first segment  of the small intestine. The duodenum is the first 10" of the small intestine

Two ducts enter the duodenum:

• one draining the gall bladder and hence the liver
• the other draining the exocrine portion of the pancreas.

From the intestinal mucosal cells, and from the liver and gallbladder. Secretions from the pancreas and bile from the gallbladder enter the duodenum through the hepatopancreatic ampulla and the sphincter of Oddi. These lie where the pancreatic duct and common bile duct join before entering the duodenum. The presence of fatty chyme in the duodenum causes release of the hormone CCK into the bloodstream. CCK is one of the enterogastrones and its main function, besides inhibiting the stomach, is to stimulate the release of enzymes by the pancreas, and the contraction of the gallbladder to release bile. It also stimulates the liver to produce bile. Consumption of excess fat results in excessive bile production by the liver, and this can lead to the formation of gallstones from precipitation of the bile salts. 

The acid in the chyme stimulates the release of secretin which causes the pancreas to release bicarbonate which neutralizes the acidity

Glomerular filtration

Kidneys receive about 20% of cardiac output , this is called Renal Blood Flow (RBF) which is approximatley 1.1 L of blood. Plasma in this flow is about 625 ml . It is called Renal Plasma Flow (RPF) .
About 20 % of Plasma entering the glomerular capillaries is filtered into the Bowman`s capsule .
Glomerular filtration rate is about 125 ml/min ( which means 7.5 L/hr and thus 180 L/day) This means that the kidney filters about 180 liters of plasma every day.

The urine flow is about 1ml/min ( about 1.5 liter /day) This means that kidney reabsorbs about 178.5 liters every day .

Filtration occurs through the filtration unit , which includes :

1- endothelial cells of glomerular capillaries , which are fenestrated . Fenestrae are quite small so they prevent filtration of blood cells and most of plasma proteins .

2- Glomerular basement membrane : contains proteoglycan that is negatively charged and repels the negatively charged plasma proteins that may pass the fenestrae due to their small molecular weight like albumin . so the membrane plays an important role in impairing filtration of albumin .

3- Epithelial cells of Bowman`s capsule that have podocytes , which interdigitate to form slits .

Many forces drive the glomerular filtration , which are :

1- Hydrostatic pressure of the capillary blood , which favours filtration . It is about 55 mmHg .

2- Oncotic pressure of the plasma proteins in the glomerular capillary ( opposes filtration ) . It is about 30 mm Hg .

3- Hydrostatic pressure of the Bowman`s capsule , which also opposes filtration. It is about 15 mmHg .

The net pressure is as follows :

Hydrostatic pressure of glomerular capillaries - ( Oncotic pressure of glomerular capillaries + Hydrostatic pressure of the Bowman capsule):
55-(35+10)
=55-45
=10 mmHg .

Te glomerular filtration rate does not depend only on the net pressure , but also on an other value , known as filtration coefficient ( Kf) . The later depends on the surface area of the glomerular capillaries and the hydraulic conductivity of the glomerular capillaries.
 

The Kidneys

The kidneys are the primary functional organ of the renal system.

They are essential in homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and the regulation of blood pressure (by maintaining salt and water balance).

They serve the body as a natural filter of the blood and remove wastes that are excreted through the urine.

They are also responsible for the reabsorption of water, glucose, and amino acids, and will maintain the balance of these molecules in the body.

In addition, the kidneys produce hormones including calcitriol, erythropoietin, and the enzyme renin, which are involved in renal and hemotological physiological processes.

Anatomical Location

The kidneys are a pair of bean-shaped, brown organs about the size of your fist. They are covered by the renal capsule, which is a tough capsule of fibrous connective tissue.

Right kidney being slightly lower than the left, and left kidney being located slightly more medial than the right.

The right kidneys lie  just below the diaphragm and posterior to the liver, the left below the diaphragm and posterior to the spleen.

Resting on top of each kidney is an adrenal gland (adrenal meaning on top of renal), which are involved in some renal system processes despite being a primarily endocrine organ.

They are considered retroperitoneal, which means that they lie behind the peritoneum, the membrane lining of the abdominal cavity.

The renal artery branches off from the lower part of the aorta and provides the blood supply to the kidneys.

 Renal veins take blood away from the kidneys into the inferior vena cava.

The ureters are structures that come out of the kidneys, bringing urine downward into the bladder.

Internal Anatomy of the Kidneys

There are three major regions of the kidney:

1.         Renal cortex

2.         Renal medulla

3.         Renal pelvis

The renal cortex is a space between the medulla and the outer capsule.

The renal medulla contains the majority of the length of nephrons, the main functional component of the kidney that filters fluid from blood.

The renal pelvis connects the kidney with the circulatory and nervous systems from the rest of the body.

Renal Cortex

The kidneys are surrounded by a renal cortex

The cortex provides a space for arterioles and venules from the renal artery and vein, as well as the glomerular capillaries, to perfuse the nephrons of the kidney. Erythropotein, a hormone necessary for the synthesis of new red blood cells, is also produced in the renal cortex.

Renal Medulla

The medulla is the inner region of the parenchyma of the kidney. The medulla consists of multiple pyramidal tissue masses, called the renal pyramids, which are triangle structures that contain a dense network of nephrons.

At one end of each nephron, in the cortex of the kidney, is a cup-shaped structure called the Bowman's capsule. It surrounds a tuft of capillaries called the glomerulus that carries blood from the renal arteries into the nephron, where plasma is filtered through the capsule.

After entering the capsule, the filtered fluid flows along the proximal convoluted tubule to the loop of Henle and then to the distal convoluted tubule and the collecting ducts, which flow into the ureter. Each of the different components of the nephrons are selectively permeable to different molecules, and enable the complex regulation of water and ion concentrations in the body.

Renal Pelvis

The renal pelvis contains the hilium. The hilum is the concave part of the bean-shape where blood vessels and nerves enter and exit the kidney; it is also the point of exit for the ureters—the urine-bearing tubes that exit the kidney and empty into the urinary bladder. The renal pelvis connects the kidney to the rest of the body.

Supply of Blood and Nerves to the Kidneys

•  The renal arteries branch off of the abdominal aorta and supply the kidneys with blood. The arterial supply of the kidneys varies from person to person, and there may be one or more renal arteries to supply each kidney.

•  The renal veins are the veins that drain the kidneys and connect them to the inferior vena cava.

•  The kidney and the nervous system communicate via the renal plexus. The sympathetic nervous system will trigger vasoconstriction and reduce renal blood flow, while parasympathetic nervous stimulation will trigger vasodilation and increased blood flow.

•  Afferent arterioles branch into the glomerular capillaries, while efferent arterioles take blood away from the glomerular capillaries and into the interlobular capillaries that provide oxygen to the kidney.

•  renal vein

The veins that drain the kidney and connect the kidney to the inferior vena cava.

•  renal artery

These arise off the side of the abdominal aorta, immediately below the superior mesenteric artery, and supply the kidneys with blood.

Exchange of gases takes place in Lungs

• A person with an average ventilation rate of 7.5 L/min will breathe in and out 10,800 liters of gas each day
• From this gas the person will take in about 420 liters of oxygen (19 moles/day) and will give out about 340 liters of carbon dioxide (15 moles/day)
• The ratio of CO₂ expired/O₂ inspired is called the respiratory quotient (RQ)
  • RQ = CO₂ out/O₂ in = 340/420 = 0.81
  • In cellular respiration of glucose CO₂ out = O₂ in; RQ = 1
  • The overall RQ is less than 1 because our diet is a mixture of carbohydrates and fat; the RQ for metabolizing fat is only 0.7
• All of the exchange of gas takes place in the lungs
• The lungs also give off large amounts of heat and water vapor

The large intestine (colon)

The large intestine receives the liquid residue after digestion and absorption are complete. This residue consists mostly of water as well as materials (e.g. cellulose) that were not digested. It nourishes a large population of bacteria (the contents of the small intestine are normally sterile). Most of these bacteria (of which one common species is E. coli) are harmless. And some are actually helpful, for example, by synthesizing vitamin K. Bacteria flourish to such an extent that as much as 50% of the dry weight of the feces may consist of bacterial cells. Reabsorption of water is the chief function of the large intestine. The large amounts of water secreted into the stomach and small intestine by the various digestive glands must be reclaimed to avoid dehydration.