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Urine:

Filtration

JoVE 10891

The function of the kidneys is to filter, reabsorb, secrete, and excrete. Every day the kidneys filter nearly 180 liters of blood, initially removing water and solutes but ultimately returning nearly all filtrates into circulation with the help of osmoregulatory hormones. This process removes wastes and toxins but is also crucial to maintain water and electrolyte levels. Most of these functions are performed by the tiny but numerous nephrons contained within the kidneys. Blood enters the renal corpuscle of the nephron through a glomerulus of capillaries. The capillaries are surrounded by a structure called the Bowman’s capsule which absorbs water and most solutes from the blood. The blood pressure from capillaries pushes these into the capsules. If the blood pressure is too high, as seen in hypertension, the capillaries can weaken and harden, reducing the ability of the kidney to filter the blood. The filtrate from the corpuscles empty into the proximal convoluted tubules and the descending portions of the Loop of Henle. Here nearly 70% of solutes—salt, glucose, amino acids, and bicarbonates—are reabsorbed into the surrounding capillaries. Circulating blood hormones involved in osmoregulation induce reabsorption of sodium, calcium, or more water if needed to increase or decrease blood pressure and regulate electrolytes. Sec

 Core: Biology

Kidney Structure

JoVE 10890

The kidneys are two large bean-shaped organs located in the upper abdomen. They filter the blood several times a day to remove toxins and rebalance water and electrolytes of the circulatory system via the renal veins. The kidneys receive blood directly from the heart via the renal arteries. These arteries enter the kidney at the hilum, the concave surface of the bean, where they branch and divide into smaller vessels and capillaries. The renal cortex is the thick outer layer of the kidney. It houses renal corpuscles, where capillaries come into close contact with the end of a renal tubule. The end of the tubule, or Bowman’s capsule, surrounds a net of capillaries that looks like a ball, the glomerulus. This unusual arrangement of the capillaries increases the surface area where the end of the renal tubule and the capillaries interact. From the Bowman’s capsule, the convoluted tubules extend into the Loop of Henle that lay in the renal medulla, the tissue beneath the renal cortex. Cortical intrusions structure the medulla into multiple renal pyramids. The apex of each pyramid points towards the hilum area, thus draining the collecting ducts into calyces in the renal pelvis. As the pelvis fills, urine is emptied into the ureter. The ureter connects the kidneys to the bladder, where urine is stored before being eliminated. The renal corp

 Core: Biology

Urea Cycle

JoVE 10892

The urea cycle describes how liver cells convert ammonia to urea. Ammonia is a toxic waste product of protein catabolism. Land animals must convert ammonia into the less toxic urea which can be safely eliminated by the kidneys through urine. Marine animals excrete ammonia directly, and the surrounding water dilutes the ammonia to safe levels.

There are five basic steps in the urea cycle: the conversion of ammonia (NH3) to carbamoyl phosphate the introduction of ornithine in the transformation of carbamoyl phosphate to citrulline the transformation of citrulline into arginosuccinate involving aspartate and chemical energy (ATP) the conversion of arginosuccinate into arginine with fumarate as a by-product the formation of urea and ornithine from arginine Notice that ornithine is used in the second step and is regenerated in the last step. Since ornithine is recycled, the urea cycle is sometimes referred to as the ornithine cycle. Elevated levels of blood ammonia, or hyperammonemia, results from an interruption of the urea cycle. This can occur at the organ level where scar tissue blocks the blood supply to the liver. Scar tissue, or cirrhosis, can result from chronic alcohol abuse, hepatitis B, or hepatitis C infection. Within the liver cells, disruption of the urea c

 Core: Biology

What is the Endocrine System?

JoVE 10875

The endocrine system sends hormones—chemical signals—through the bloodstream to target cells—the cells the hormones selectively affect. These signals are produced in endocrine cells, secreted into the extracellular fluid, and then diffuse into the blood. Eventually, they diffuse out of the blood and bind to target cells which have specialized receptors to recognize the hormones. While most hormones travel through the circulatory system to reach their target cells, there are also alternate routes to bring hormones to target cells. Paracrine signaling sends hormones out of the endocrine cell and into the extracellular fluid where they affect local cells. In a form of paracrine signaling, called autocrine signaling, hormones secreted into the extracellular fluid affect the cell that secreted them. Another type of signaling, synaptic signaling, involves the release of neurotransmitters from neuron terminals into the synapse—a specialized junction that relays information between neurons—where they bind to receptors on neighboring neurons, muscle cells, and glands. In neuroendocrine signaling, neurosecretory cells secrete neurohormones that travel through the blood to affect target cells. Overall, endocrine signaling has a slower effect than other types of signaling because it takes longer for hormones to reach the target cel

 Core: Biology

The Parasympathetic Nervous System

JoVE 10839

The parasympathetic nervous system is one of the two major divisions of the autonomic nervous system. This parasympathetic system is responsible for regulating many unconscious functions, such as heart rate and digestion. It is composed of neurons located in both the brain and the peripheral nervous system that send their axons to target muscles, organs, and glands.

Activation of the parasympathetic system tends to have a relaxing effect on the body, promoting functions that replenish resources and restore homeostasis. It is therefore sometimes referred to as the “rest and digest” system. The parasympathetic system predominates during calm times when it is safe to devote resources to basic “housekeeping” functions without a threat of attack or harm. The parasympathetic nervous system can be activated by various parts of the brain, including the hypothalamus. Preganglionic neurons in the brainstem and sacral part of the spinal cord first send their axons out to ganglia—clusters of neuronal cell bodies—in the peripheral nervous system. These ganglia contain the connections between pre- and postganglionic neurons and are located near the organs or glands that they control. From here, postganglionic neurons send their axons onto target tissues—generally smooth muscle, cardiac muscle, or glands. Typic

 Core: Biology

Protein Digestion

JoVE 10833

Protein digestion begins in the stomach, where the highly acidic environment can easily disrupt protein structure by exposing the peptide bonds of polypeptide chains. After polypeptide chains are broken into individual amino acids by a series of digestive enzymes, the amino acids are transported to the liver via the bloodstream to produce energy.

Pepsin is a protease, or protein-digesting enzyme, that is produced in the stomach and is one of the main digestive enzymes in the human digestive system. Working in conjunction with chymotrypsin and trypsin released in the small intestine, pepsin severs the links between specific types of amino acids to form shorter polypeptide chains. Other enzymes, called peptidases, then split off one amino acid at a time from the ends of these polypeptide chains. The small intestine can easily absorb the resulting amino acids. The liver plays an essential role in the metabolism of proteins. Liver cells alter digested amino acids from the small intestine so that they can be used to produce energy or make carbohydrates and fats. A byproduct of this process is a toxic substance called ammonia, which the liver then converts into a much less toxic substance called urea. Urea is then released into the blood and transported to the kidneys, which excrete urea out of the body through urine.

 Core: Biology

Pedigree Analysis

JoVE 10775

A pedigree is a diagram displaying a family’s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or recessive, (2) the type of chromosome, autosomal or sex, a trait is linked to, (3) genotypes of family members, and (4) probabilities of phenotypes in future generations. For families with a history of autosomal or sex-linked diseases, this information can be crucial to family planning. In various plant and animal species, scientists study the inheritance of phenotypes, or traits, using carefully controlled mating experiments called crosses. For example, monohybrid crosses can establish trait dominance or recessiveness, and test crosses can determine the genotype (homozygous or heterozygous) of an organism exhibiting a known dominant phenotype. Humans, however, cannot be ethically or feasibly crossed. Therefore, researchers analyze pedigrees, or family trees, to understand how human traits and diseases are inherited. Pedigrees display a family’s history of a trait across generations and family members. Using the same principles that apply to crosses to analyze reproductive events that have already occurred, information about trait heritability can be inferred. On a typical pedigree, squares represent males and circles represent females. Shaded squares or circles signify the presence of a trait of intere

 Core: Biology

What is Metabolism?

JoVE 10725

Metabolism represents all of the chemical activity in a cell, including reactions that build molecules (anabolism) and those that break molecules down (catabolism). Anabolic reactions require energy, whereas catabolic reactions provide it. Thus, metabolism describes how cells transform energy through a variety of chemical reactions, which are often made more efficient with the help of enzymes. Metabolism is the management of energy in cells and provides three key functions: converting food into energy to run various cellular processes, producing energy to build cell components, and removing waste products. To produce energy, macromolecules from food must be broken down into smaller molecules—through a catabolic pathway. This, in turn, provides energy to construct larger molecules from smaller building blocks—through an anabolic pathway. In other words, the potential energy in food—comprised of the chemical energy stored in the bonds between atoms—can be converted into kinetic energy that can be used for cellular reactions. Enzymes are essential molecular tools in metabolic pathways, as they greatly speed up many chemical reactions by reducing the amount of required energy. Catabolism is the breakdown of macromolecules for any purpose. This inc

 Core: Biology

Observation and Inspection

JoVE 10119

Source: Jaideep S. Talwalkar, MD, Internal Medicine and Pediatrics, Yale School of Medicine, New Haven, CT


Observation and inspection is fundamental to physical examination and begins at the first point of contact with a patient. While observation and inspection are often used interchangeably, observation is a general term …

 Physical Examinations I
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