GLAUCOMA

 

INTRODUCTION:  The presence of aqueous humor in the anterior cavity of the eye creates a pressure called intraocular pressure. An increase in this pressure is an important risk factor for glaucoma, which is now defined as a group of disorders that damage the optic nerve and cause loss of vision.  Other risk factors include high blood pressure and diabetes.

PATHOPHYSIOLOGY:  In the most common form of glaucoma, aqueous humor is not reabsorbed properly into the canal of Schlemm. Increased pressure in the anterior cavity is transmitted to the lens, the vitreous humor, and the retina and optic nerve. As pressure on the retina increases, halos may be seen around bright lights, and peripheral vision is lost. Frequently, however, there are no symptoms.

SIGNS AND SYMPTOMS:  A person with glaucoma may not notice the shrinking visual field in one eye before vision loss is far advanced. This happens because the brain will suppress a faulty image from one eye that it cannot easily integrate with the normal image of the other eye. When both eyes are affected, the person may not become aware of the gradual loss of peripheral vision, because close work such as reading does not require the edges of the visual fields.

PREVENTION AND TREATMENT: Glaucoma may often be controlled with medications that constrict the pupil and flatten the iris, thus opening up access to the canal of Schlemm. If these or other medications are not effective, laser surgery may be used to create a larger drainage canal.  Anyone over the age of 40 should have a test for glaucoma; anyone with a family history of glaucoma should have this test annually, as should those with diabetes or high blood pressure. If diagnosed early, glaucoma is treatable, and blindness can usually be prevented.

 

RELATED;

1.  BLOOD PRESSURE AND HYPERTENSION

2. DIABETES MELLITUS

3. MEDICAL CONDITIONS

4. REFERENCES

LIVER

 

INTRODUCTION: The liver consists of two large lobes, right and left, and fills the upper right and center of the abdominal cavity, just below the diaphragm. The structural unit of the liver is the liver lobule, a roughly hexagonal column of liver cells (hepatocytes). Between adjacent lobules are branches of the hepatic artery and portal vein. The capillaries of a lobule are sinusoids, large and very permeable vessels between the rows of liver cells. The sinusoids receive blood from both the hepatic artery and portal vein, and it is with this mixture of blood that the liver cells carry out their functions.

BLOOD SUPPLY OF THE LIVER: The hepatic artery brings oxygenated blood, and the portal vein brings blood from the digestive organs and spleen. Each lobule has a central vein. The central veins of all the lobules unite to form the hepatic veins, which take blood out of the liver to the inferior vena cava. The cells of the liver have many functions, but their only digestive function is the production of bile.

ROLE OF BILE IN DIGESTION: Bile enters the small bile ducts, called bile canaliculi, on the liver cells, which unite to form larger ducts and finally merge to form the hepatic duct, which takes bile out of the liver. The hepatic duct unites with the cystic duct of the gallbladder to form the common bile duct, which takes bile to the duodenum. Bile is mostly water and has an excretory function in that it carries bilirubin and excess cholesterol to the intestines for elimination in feces. The digestive function of bile is accomplished by bile salts, which emulsify fats in the small intestine. Emulsification means that large fat globules are broken into smaller globules. This is mechanical, not chemical, digestion; the fat is still fat but now has more surface area to facilitate chemical digestion. Production of bile is stimulated by the hormone secretin, which is produced by the duodenum when food enters the small intestine.

RELATED;

1. HEPATIC PORTAL CIRCULATION

2. DIGESTION OF FOOD

3. HEPATITIS

4.  FUNCTIONS OF THE LIVER

5.  LIVER FAILURE

6.  ANATOMY AND PHYSIOLOGY

REFERENCES

FUNCTIONS OF THE LIVER

 

INTRODUCTION:  The liver is a remarkable organ, and only the brain is capable of a greater variety of functions. The liver cells also known as hepatocytes, produce many enzymes that catalyze many different chemical reactions. These reactions are the functions of the liver. As blood flows through the sinusoids (capillaries) of the liver, materials are removed by the liver cells, and the products of the liver cells are secreted into the blood.

1. CARBOHYDRATE METABOLISM:  As you know, the liver regulates the blood glucose level. Excess glucose is converted to glycogen in a process known as glycogenesis when blood glucose is high; the hormones insulin and cortisol facilitate this process. During hypoglycemia or stress situations, glycogen is converted back to glucose in a process known as glycogenolysis to raise the blood glucose level. Epinephrine and glucagon are the hormones that facilitate this process.  The liver also changes other monosaccharides to glucose. Fructose and galactose, for example, are end products of the digestion of sucrose and lactose. Because most cells, however, cannot readily use fructose and galactose as energy sources, they are converted by the liver to glucose, which is easily used by cells.

2. AMINO ACID METABOLISM:  The liver regulates blood levels of amino acids based on tissue needs for protein synthesis. Of the 20 different amino acids needed for the production of human proteins, the liver is able to synthesize 12, called the non essential amino acids. The other eight amino acids, which the liver cannot synthesize, are called the essential amino acids. In this case, “essential” means that the amino acids must be supplied by our food, because the liver cannot manufacture them.

3. LIPID METABOLISM:  The liver forms lipoproteins, which as their name tells us, are molecules of lipids and proteins, for the transport of fats in the blood to other tissues. The liver also synthesizes cholesterol and excretes excess cholesterol into bile to be eliminated in feces. Fatty acids are a potential source of energy, but in order to be used in cell respiration they must be broken down to smaller molecules. In the process of beta-oxidation, the long carbon chains of fatty acids are split into two-carbon molecules called acetyl groups, which are simple carbohydrates.

These acetyl groups may be used by the liver cells to produce ATP or may be combined to form ketones to be transported in the blood to other cells. These other cells then use the ketones to produce ATP in cell respiration.

4. SYNTHESIS OF PLASMA PROTEINS: The liver synthesizes many of the proteins that circulate in the blood. Albumin, the most abundant plasma protein, helps maintain blood volume by pulling tissue fluid into capillaries. The clotting factors are also produced by the liver. These, include prothrombin, fibrinogen, and Factor 8, which circulate in the blood until needed in the chemical clotting mechanism. The liver also synthesizes alpha and beta globulins, which are proteins that serve as carriers for other molecules, such as fats, in the blood.

5. FORMATION OF BILIRUBIN:  This is another familiar function: The liver contains fixed macrophages that phagocytize old red blood cells (RBCs). Bilirubin is then formed from the heme portion of the hemoglobin. The liver also removes from the blood the bilirubin formed in the spleen and red bone marrow and excretes it into bile to be eliminated in feces.

6. PHAGOCYTOSIS BY KUPFFER CELLS: The fixed macrophages of the liver are called Kupffer cells (or stellate reticuloendothelial cells). Besides destroying old RBCs, Kupffer cells phagocytize pathogens or other foreign material that circulate through the liver. Many of the bacteria that get to the liver come from the colon. These bacteria are part of the normal flora of the colon but would be very harmful elsewhere in the body. The bacteria that enter the blood with the water absorbed by the colon are carried to the liver by way of portal circulation. The Kupffer cells in the liver phagocytize and destroy these bacteria, removing them from the blood before the blood returns to the heart.

7. STORAGE: The liver stores the fat-soluble vitamins A, D, E, and K, and the water-soluble vitamin B12.  Also stored by the liver are the minerals iron and copper. You already know that iron is needed for hemoglobin and myoglobin and enables these proteins to bond to oxygen. Copper (as well as iron) is part of some of the proteins needed for cell respiration, and is part of some of the enzymes necessary for hemoglobin synthesis.

8. DETOXIFIFICATION:  The liver is capable of synthesizing enzymes that will detoxify harmful substances, that is, change them to less harmful ones. Alcohol, for example, is changed to acetate, which is a two carbon molecule (an acetyl group) that can be used in cell respiration. Medications are all potentially toxic, but the liver produces enzymes that break them down or change them. When given in a proper dosage, a medication exerts its therapeutic effect but is then changed to less active substances that are usually excreted by the kidneys. An overdose of a drug means that there is too much of it for the liver to detoxify in a given time, and the drug will remain in the body with possibly harmful effects.

 

RELATED;

1.  CORTISOL

2. GLUCAGON

3. EPINEPHRINE

4. PLASMA PROTEINS

5. HEPATIC PORTAL CIRCULATION

6. HEPATITIS

REFERENCES

 

TISSUES

INTRODUCTION: A tissue is a group of cells with similar structure and function. The tissue contributes to the functioning of the organs in which it is found. The four groups of tissues are epithelial, connective, muscle, and nerve tissue.

EPITHELIAL TISSUE: Epithelial tissues are found on surfaces as either coverings for the outer surfaces, or linings for the inner surfaces. Because they have no capillaries of their own, epithelial tissues receive oxygen and nutrients from the blood supply of the connective tissue beneath them. Many epithelial tissues are capable of secretion and may be called glandular epithelium, or more simply, glands.  Classification of the epithelial tissues is based on the type of cell of which the tissue is made, its characteristic shape, and the number of layers of cells. There are three distinctive shapes: squamous cells are flat, cuboidal cells are cube shaped, and columnar cells are tall and narrow. “Simple” is the term for a single layer of cells, and “stratified” means that many layers.

SIMPLE SQUAMOUS EPITHELIUM: Simple squamous epithelium is a single layer of flat cells. These cells are very thin and very smooth. The alveoli (air sacs) of the lungs are simple squamous epithelium. The thinness of the cells permits the diffusion of gases between the air and blood. Another location of this tissue is capillaries, the smallest blood vessels. Capillary walls are only one cell thick, which permits the exchange of gases, nutrients, and waste products between the blood and tissue fluid. The interior surface of capillaries is also very smooth. These cells continue as the lining of the arteries, veins, and heart; this is important because it prevents abnormal blood clotting within blood vessels.

STRATIFIED SQUAMOUS EPITHELIUM: Stratified squamous epithelium consists of many layers of mostly flat cells, although lower cells are rounded. Mitosis takes place in the lowest layer to continually produce new cells to replace those worn off the surface. This type of epithelium makes up the epidermis of the skin, where it is called keratinizing because the protein keratin is produced, and the surface cells are dead. Stratified squamous epithelium of the non-keratinizing type lines the oral cavity, the esophagus, and, in women, the vagina. In these locations the surface cells are living and make up the mucous membranes of these organs. In all of its body locations, this tissue is a barrier to microorganisms because the cells of which it is made are very close together.

TRANSITIONAL EPITHELIUM: Transitional epithelium is a type of stratified epithelium in which the surface cells change shape from round to squamous. The urinary bladder is lined with transitional epithelium. When the bladder is empty, the surface cells are rounded. As the bladder fills, these cells become flattened. Transitional epithelium enables the bladder to fill and stretch without tearing the lining.

SIMPLE CUBOIDAL EPITHELIUM: Simple cuboidal epithelium is a single layer of cube-shaped cells. This type of tissue makes up the functional units of the thyroid gland and salivary glands. These are examples of glandular epithelium; their function is secretion. In these glands the cuboidal cells are arranged in small spheres and secrete into the cavity formed by the sphere. In the thyroid gland, the cuboidal epithelium secretes the thyroid hormones; thyroxine is an example. In the salivary glands the cuboidal cells secrete saliva. Cuboidal epithelium also makes up portions of the kidney tubules. Here the cells have microvilli, and their function is the reabsorption of useful materials back to the blood.

SIMPLE COLUMNAR EPITHELIUM: Columnar cells are taller than they are wide and are specialized for secretion and absorption. The stomach lining is made of columnar epithelium that secretes gastric juice for digestion. The lining of the small intestine secretes digestive enzymes, but these cells also absorb the end products of digestion from the cavity of the intestine into the blood and lymph. To absorb efficiently, the columnar cells of the small intestine have microvilli, which you may recall are folds of the cell membrane on their free surfaces. These microscopic folds greatly increase the surface area for absorption. Yet another type of columnar cell is the goblet cell, which is a unicellular gland. Goblet cells secrete mucus and are found in the lining of the intestines and the lining of parts of the respiratory tract such as the trachea.

CILIATED EPITHELIUM: Ciliated epithelium consists of columnar cells that have cilia on their free surfaces. Ciliated epithelium lines the nasal cavities, larynx, trachea, and large bronchial tubes. The cilia sweep mucus, with trapped dust and bacteria from the inhaled air, toward the pharynx to be swallowed. Bacteria are then destroyed by the hydrochloric acid in the stomach. The air that reaches the lungs is almost entirely free of pathogens and particulate pollution. Another location of ciliated epithelium in women is the lining of the fallopian tubes. The cilia here sweep the ovum, which has no means of self-locomotion, toward the uterus.

RELATED;

1.  THE CELL MEMBRANE

2.  ANATOMY AND PHYSIOLOGY

REFERENCES