The Urinary System

(How kidneys filter blood)

Water, which makes up 60% of our body weight, circulates mainly in the blood, which transports nutrients and waste. The urinary system allows you to control the volume of water in the body and eliminate certain urinary substances. The kidneys function like real filters, capable of extracting wasted blood without depriving it of nutrients. The secreted urine is stored in the bladder and then evacuated through the urethra. To compensate for this fluid loss, an adult should drink two liters of water a day

Urinary system organs

Located on both sides of the aorta and vena cava, the kidneys are powered by the renal arteries, which acts to filter the blood and produce urine, and is transported to the bladder by both ureters. The urethra, which removes urine from the bladder, is longer in men than in women

Functions of the urinary system

The kidneys are glandular organs that produce an ultrafiltrate called urine which is transported from the ureters (muscle tubes) to the urinary bladder for storage. Urine is expelled to the external environment through the urethra. The urinary system performs a number of functions:

• Elimination of metabolic waste and toxins (mainly nitrogen waste from the breakdown of proteins and nucleic acids), but we have several organs that have an excretory function in addition to the kidneys:

• kidneys
• Skin, sweat glands remove body water, minerals, some nitrogen waste (ammonia)
• Lungs, rid the body of CO2 from the energy metabolism of cells
• Liver, the liver excretes bile pigments, salts, calcium, some toxins

• Helps regulate volume and blood pressure, blood pressure is directly affected by the volume of fluids retained or removed from the body:

Excessive salts promote a greater volume of water retention: increases blood pressure (Hypertension), and vice versa, dehydration at a lower volume: lowers blood pressure

• Regulation of electrolytes and body pH

• Regulates erythropoiesis, the kidneys produce hormone erythropoietin which regulates erythropoiesis:

Hypoxic: secretes more erythropoietin Excess O2 inhibits hormone production

• Helps the absorption of calcium, affects the absorption of calcium from the intestine by helping to activate the vitamin D circulating in the blood

• Elimination of excess nutrients and excess hormones

It has important endocrine functions which include the following:

• Erythropoietin is produced and secreted by the kidney to regulate erythropoietic cells in the marrow
• Renin is part of the renin-angiotensin-aldosterone system which controls blood pressure and volume; Renin is released by the kidney into the blood circulatory system, where angiotensinogen is divided into the circulation to release angiotensin I
• Vitamin D: part of the synthetic pathway of this hormone happens in the kidney

Anatomy of the urinary system

Kidneys: (clean and filter blood)

The kidneys are small organs, take the shape of the beans. It's protected by a fibrous capsule and it is surrounded by a layer of fatty tissue, its length is about 11 cm. They consist of an external layer, the cortex and an internal region, the medulla, in which conical structures called "pyramids" appear. The pyramids are made up of many renal tubules that converge to form collection tubules, which are emptied into small and large calyxes. The calyxes receive the urine produced by the nephrons (functional units located both in the cortex and in the marrow) and evacuate it through the cradle, a cavity that opens into the ureter

The coupled reddish organs, just above the waist in the posterior wall of the abdomen, partially protected by the ribs 11 and 12, the right kidney sitting lower than the left kidney, receive 20 to 25% of the cardiac output at rest, consume from 20 25% of O2 used by the body at rest

• Adrenal cortex The adrenal gland consists of an adrenal medulla and an adrenal cortex that are embryologically, histologically and functionally different, although they are largely combined. The adrenal medulla is derived from the neural crest, known as ectoderm. The adrenal cortex derives from the cells of the mesonephric tubules that dissociate and migrate to the position of the adrenal gland when the mesonephri degenerate

Internal anatomy of the kidney:

The parenchyma (distinctive cells) of the kidney is divisible into (1) cortex and (2) marrow

• The cortex (outer region) is widely divisible into alternating medullary rays and cortical labyrinths. The medullary rays are rich in straight tubules and collection ducts; Cortical labyrinths are rich in renal corpuscles, convoluted tubules and collection tubules. The alternating order of medullary rays and cortical labyrinths gives the kidney its striated appearance in the macroscopic section

• Medulla In organisms with multilobed kidneys, such as humans, the medulla (internal region) is divisible into alternating pyramids and renal columns

The tubular composition of a medullary pyramid varies between its internal and external portions. In the external portion (adjacent to the bark) thick tubules predominate; on the contrary, the thin tubules are more frequently found in the internal portion. Each pyramid drains into its papillae in a smaller chalice; Several smaller glasses come together to form a larger glass. In turn, the main calices come together to form the kidney basin which is drained from the ureter Kidneys: are made up of units arranged radially called lobes. Each lobe is made up of a cap-shaped cortical tissue (adjacent cortex and renal columns) that encloses the base of the pyramid-shaped medullary tissue called the renal pyramid. A lobe is a subdivision of a lobe consisting of a central medullary radius and its surrounding cortical material. These divisions are helpful in understanding the arterial nomenclature of the kidney

Blood and nerve supply:

The blood supply to the kidney passes through the renal arteries. The main renal artery undergoes a series of ramifications within the kidney up to the form of afferent arterioles

Arterial: renal artery, interlobular arteries, arched arteries, interlobular arteries, afferent arteries, renal corpuscle (capillaries), Efferent arterioles, peritubular capillary network (for cortical nephrons)  or rectal vessel (for juxtamedullary nephrons)

Venous: consists peritubular capillary network, arched veins, interlobular veins and renal vein

Vascular supply:

• The renal artery enters the kidney organ through the hilum

• Branch of the renal artery (inside the renal pelvis) to form lobar arteries

• Each lobar artery enters the renal parenchyma and runs along the renal spine as interlobular arteries

• At the corticomedullary junction, the interlobar artery branch forms arched arteries

• The arched arteries follow a path along the junction that leads, at regular intervals, to the interlobular arteries, which enter the cortex

• Each interlobular artery gives rise to a short afferent arteriole that enters the renal corpuscle, from which the individual efferent arterioles emerge

• Efferent arterioles give rise to a network of capillaries that are located around the nephron tubules called peritubular capillaries

Venous drainage:

• Peritubular capillary drainage into the interlobular veins, or directly into the arched veins

• Capsular capillary drainage into the interlobular veins, therefore into the subcapsular veins

• The interlobular veins drain into the arched veins and then into the interlobular veins that run the length of the renal columns to form the lobular veins within the renal pelvis

• The lobular veins drain into the renal vein, which leaves the kidney in the hilum to join the caudal vena cava

• Note: in some species, the renal capsule is drained from several capsular veins directly into the renal vein

Nerve Supply :

The muscle of the glomerular arterioles, which is smooth receives sympathetic innervation

Functions of the components of the nephron:

The functional part of the renal is the nephron. A nephron consists of a glomerulus and, in succession, several tubular segments. The collection tubules of various nephrons gradually join together to form collection ducts that join with other collection ducts and finally empty their contents into a smaller calyx through the duct in the papillae

Two main parts of the nephron:

 • Renal corpuscle

Plasma filtration site, consist of two components

• Glomerulus

•  Locking of capillary handles
•  Powered by afferent arterioles
•  Drained from the efferent arteriole

• Glomerular capsule (Bowman), double-walled cup lined with a single external wall of the squamous epithelium (parietal layer) separated from the internal wall (visceral layer = podocytes) from the capsular space (Bowman)

• Renal tubule

•  Where the filtered fluid passes from the capsule
•  Proximal shaped tubule (PCT)
•  Cockerel ring (nephron ring) - Distal convoluted tubule (DCT)
•  Short connecting pipes - Collection pipes
•  Papillary duct • then to the lower calyx • 30 porridge / papillae

Nephrons: from blood to urine

Each kidney comprises approximately one million nephrons, filtering units and blood secretion. Blood enters through an afferent arteriole which is divided into numerous capillaries to form a glomerulus, a small sphere wrapped in a Bowman capsule. Some component substances in the blood (water, mineral salts, glucose) pass through the capillary wall and form a liquid called filtrate. The capillaries are reassembled into an efferent arteriole which leaves the glomerulus. For its part, the filtrate borrows a renal tubule that wraps itself in the cortex and medulla exchanging substances with the peritubular capillaries. These exchanges permit to reabsorb some useful products throught the blood. It is estimated that out of 180 liters of filtrate produced daily, about 179 liters are reabsorbed. What remains of the filtrate forms the urine, which is drained into the glasses by Bellini's tubules

Ureters: (tubes that carry urine to the bladder)

The ureters are muscle tubes that connect the renal pelvis to the urinary bladder (the extensions of the renal pelvis enter the bladder medially from the back, carry urine to the bladder, mainly peristalsis, but the hydrostatic pressure of gravity helps humans)

Transitional epithelium

• Aligns the ureter and bladder (relaxed state)

• Allows volume changes

• Impermeable to salt and water

• Look for: - Domed, protruding - Eosinophilic - Flatten as the bladder dilates

Urinary bladder: (stores urine until eliminated)

Before eliminated, the urine is stored in the bladder temporarily. This pocket, made of tissue muscles, has a spherical shape when full, but empties. The bladder can hold up to 500 ml on average, but the urination reflex (urine production) appears to reach 200 to 400 ml. The muscle bladder contracts, while the internal sphincter relaxes, causing the urine to evacuate through the urethra. However, a voluntarily controlled external sphincter helps block urination

The histological structure of the calyxes, renal pelvis, ureter and urinary bladder is very similar and each consists of a lumen surrounded by a three-layer wall (tunics): mucous membrane, muscle and adventitia / serous. The mucosa is lined with a transition epithelium on a lamina propria of irregular connective tissue. The transition epithelium is impermeable to water and salts. Musculature is a bilaminar smooth muscle layer with internal and external longitudinal circular bundles (but see the urinary bladder, below). It produces peristalsis to move urine. Adventitia is the outer layer of connective tissue. If it is covered with peritoneum (mesothelium) it is known as serous

The muscle layer forms a detrusor muscle and consists of smooth muscle bundles arranged in a complex mesh characteristic of all the expulsion organs. At the distal end of the bladder, the muscle thickens to form the internal urethral sphincter

Urethra: (removes urine from the body)

The urethra is a fibromuscular tube that connects the bladder to the external urethral opening. It is sexually dimorphic

The urethra develops from the urogenital sinus. Development is gender specific:

• In women, the central region of the urogenital sinus becomes the urethra
• In men, the pelvic urethra develops from the central region of the urogenital sinus and the penile urethra develops from the lengthening of the caudal end of the urogenital sinus

Urinalysis

The kidneys perform their homeostatic functions of controlling the composition of the body's internal fluids, the by-product of these activities is urine, urine contains a high concentration of solutes. In a healthy person, its volume, pH and solute concentration vary according to the needs of the body, during some pathologies, the characteristics of the urine can change dramatically

Physical properties of urine:

Transparency: it is clear, it indicates the lack of large solutes, such as plasma proteins or blood cells, may be affected by bacterial metabolism in older urine samples

Color: from light yellow to amber, due to urochromatic pigments as a by-product of bile metabolism

Normal = amber-yellow (from the decomposition of hemoglobin)

Influenced by:

Solute relationship

! > solute conc

= dark yellow to brownish

! <solute conc

= less colorless color

Diet (e.g. beetroot)

Blood in the urine

PH: 4.6 to 8.0 with an average of 6.0, due to H + in the urine

Normal urine is slightly acidic: 5.0 - 7.8 i

Influenced by: diet e.g. rich in protein! sour vegetables!

alkaline metabolic disorders:lungs, kidneys, digestive system, etc

Specific gravity: (a measure of solutes dissolved in solution) ranges from 1.001 to 1.035, due to the 5% composition of solutes in normal urine

Volume: 1-2 liters per day (about 1% of the filtration input)

Normal = 1000 - 1800 ml / day (2-3.5 pints)

Influenced by: blood pressure blood volume temperature diuretics mental state

Cells and foundries

Normally finds epithelial cells and some bacterial cells

Bacteria <100-1000 / ml = contamination from normal flora> 100,000 / ml = indicate active colonization of the urinary system

The presence of red and white blood cells is almost always a pathological inflammation of the urinary organs

Abnormal components of urine: (chemical properties)

• Albumin: a large plasma protein that must not escape from the glomerulus; When present, it is called albuminuria, which can be due to a kidney infection called glomerulonephritis

• Protein: usually too large to filter

• The presence indicates a greater permeability of the glomerular membrane due to: lesions, hypertension, irritation, toxins

• Glucose: nutrient molecules that should have been reabsorbed (in the case of high carbohydrate diets, a small amount of glucose is found in the urine)

• Normally everything is filtered and all reabsorbed bodies are reabsorbed as needed
• When it appears in the urine it indicates high concentrations of sugar in the blood: symptom of diabetes mellite

• Blood or erythrocytes: no blood cell must escape from the glomerulus or be present in the urine (except for bleeding related to menstruation); When present, it is called hematuria, which can be caused by glomerulonephritis, hemolytic anemia or urinary tract infections

• Hemoglobin: pigmentary protein that should normally be closed in the erythrocytes and not escape from the glomerulus; When present, it is called hemoglobinuria, which may indicate hemolytic anemia

• Leukocytes: large white blood cells that should not be present in the urine (except in urinary tract infections in which leukocytes are present to fight infections); When present, it is called pyuria, which can be caused by glomerular nephritis, urinary tract infection or intense exercise

• Ketones: due to the metabolism that can occur in small quantities, but not in large quantities in the urine; When present, it is called Kentonuria, which can indicate some infections in the urinary system

• Produced when excessive amounts of fat are catabolized
• Large quantities can be caused by: diabetes hunger diet, there is too few carbohydrates in the diet

• Bilirubin: a bile pigment that is normally recycled into lipid metabolism; When present, it is known as bilirubinuria, which may be due to an abnormal lipid metabolism or some infections of the urinary system

Urinary System Disorders

More severe urinary system disorder:

Nephrons can regenerate and restore kidney function after a short-term injury, or individual nephrons can widen to compensate: a person can survive on only 1/3 of a kidney when 75% is lost, the rest cannot maintain results of homeostasis because azotemia and acidosis can also lead to anemia

• Cystitis (= bladder infection)
• Kidstones

There are some kidney and urinary tract disorders that are commonly found in routine clinical practice. The frequency of occurrence of these disorders is more or less similar in many parts of the world with small variations depending on environmental, hereditary and local factors

• Obstructive uropathy / nephropathy

• Urinary tract infection

• Kidney failure

• Injuries that take up space

• Renal / renovascular hypertension

• Injury to the urinary tract

• Congenital anomalies

• Renal transplant dysfunction (rejection, acute tubular necrosis, etc.)