Stanbridge - T1 - Physiology - W9 - Urinary & Reproductive Systems

Urinary System: Fox Chapter 17

• Objectives include listing the urinary system's components and understanding its functions. Describing the filtrate pathway in the nephron is also an objective.

• The main components of the urinary system are kidneys, ureters, bladder, and urethra. The kidneys produce urine, ureters transport it, the bladder stores urine, and the urethra excretes it.

• Kidneys are located between the 12th rib and L3 vertebrae. The right kidney sits slightly lower than the left kidney due to the liver's position.

• Kidney functions include excretion (removing metabolic waste and toxins), maintaining acid-base balance, regulating blood pressure, red blood cell production, and blood glucose regulation.

• Ureters are long, slender muscular tubes that transport urine from the kidneys to the bladder via gravity and peristalsis.

Anatomy of a Kidney

• The kidney's outer layer is the renal capsule, which protects from infections. The renal cortex is the outer portion and the medulla contains tubes responsible for urine formation.

• Renal pyramids are cone-shaped structures within the medulla. Renal pelvis collects urine from the pyramids' tips.

• Calyces (singular: calyx) are extensions of the renal pelvis. They collect urine from the pyramids and move it to the renal pelvis.

Nephrons

• Nephrons are the structural and functional units of the kidneys. There are over one million per kidney.

• Nephrons create filtrate from blood, recover needed chemicals, and secrete waste into the filtrate, which becomes urine.

• Nephrons' components are Bowman's capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and the collecting duct (multiple nephrons share a collecting duct).

Filtrate

• Filtrate, flowing through the nephron, should not contain large proteins or red blood cells which is a normal condition.

• It's composed of water, salts, glucose, amino acids, creatine, and other substances.

Renal Tubule

• The renal tubule is the part of the nephron where filtrate moves before entering the collecting duct.

• The three parts of the renal tubule are the proximal convoluted tubule, nephron loop, and distal convoluted tubule.

Juxtaglomerular Apparatus

• The juxtaglomerular apparatus is where the distal convoluted tubule meets the afferent arteriole and contains specialized cells that regulate blood pressure.

Processes of Urine Formation

• Urine formation has four main processes: glomerular filtration, reabsorption, secretion, and excretion

• Glomerular filtration filters the blood in the Bowman's capsule. Reabsorption takes materials out of the filtrate and puts them back in the blood. The third step, secretion, transfers materials from the blood to the filtrate. Excretion removes urine from the body.

Pathway of Filtrate

• The pathway if filtrate begins with the afferent arteriole. Filtrate travels through Bowman's capsule, proximal convoluted tubule, nephron loop, distal convoluted tubule, collecting duct, calyx, renal pelvis, ureter, urinary bladder, and urethra.

Counter-Current Multiplier in the Loop of Henle

• The loop of Henle's descending limb is permeable to water, reabsorbing it back into the bloodstream.

• The ascending limb is impermeable to water but actively transports sodium, chloride, and potassium out of the filtrate and into the blood. This process creates a concentration gradient for water reabsorption in the loop.

Overall Reabsorption and Secretion in the Nephron

• The blue parts of a diagram represent reabsorption, taking substances from the filtrate and putting them back into the blood.

• The green parts of a diagram represent secretion, moving substances from the blood to the filtrate.

What Urine is Composed Of

• Urine is mostly water (95%).

• Other components include urea, uric acid, and creatine .

The Urinary Bladder

• The bladder is a temporary urine storage organ. It has multiple layers, including a mucous membrane, transitional epithelium (allows the wall to stretch), rugae (folds), and a three-layered coat of involuntary muscle tissue.

The Urethra

• The urethra is a tube for excreting urine from the bladder. It consists of multiple layers. A mucous membrane helps it stretch, and rugae - or folds- provide more room to stretch. A three-layered coat helps with involuntary muscle tissue.

Excretion

• Excretion: Urination (voiding) takes place as urine travels from renal tubules to the collecting duct to the renal calyx to the pelvis to the bladder (for storage) to the urethra.

Physiology of Micturition

• Bladder storage happens constantly at about 400-600 ml capacity, and accommodates filling. Sensory stretch receptors first detect filling, then the guarding reflex of the external sphincter occurs as the bladder fills further.

• For voiding the stretch receptors produce a strong sensation. This triggers relaxation of the PFM and internal sphincter. The detrusor muscle contracts, and urination occurs when outlet pressure is less than bladder pressure.

Normal Bladder Health

• An average healthy person urinates 5-7 times in a day with 8-12 oz urine output each time.

• The average time interval between voiding is 2-3 hours.

• Normally, a person under 65 urinates 0 times at night and 1-2 times for people over 65.

Types of Urinary Incontinence

• Incontinence is the involuntary loss of urine, which isn't normal. Common types include stress, urge, mixed, and functional incontinence, as well as neurogenic bladder.

Hormonal Regulation in the Nephrons

• Parathyroid hormone (PTH) is secreted from parathyroid glands. It mainly acts in the distal convoluted tubule (DCT) to increase calcium reabsorption into the body.

• Antidiuretic hormone (ADH) is produced by the hypothalamus and released by the posterior pituitary gland. It is released in response to high blood solute concentration or low blood volume.

• ADH targets the kidneys to increase water reabsorption. It works by inserting aquaporins in the collecting duct cells, which increases water's permeability, so more water is reabsorbed back into the blood.

Sodium Regulation

• Sodium (Na+) is the primary extracellular solute. It's crucial for osmotic pressure and excitable cell function.

• Distal convoluted tubule and collecting duct principal cells regulate Na+ reabsorption, and hormones ADH and aldosterone assist in this process.

• Atrial natriuretic peptide (ANP) helps reduce blood pressure and blood volume by inhibiting sodium and water retention.

Potassium Balance

• Potassium balance is controlled by how much of potassium is filtered, how much is reabsorbed, and if any is secreted. Aldosterone is secreted in response to elevated potassium levels and will increase the excretion (or output) of potassium from the body.

Reproductive System: Fox Chapter 20

• Objectives include listing male and female gonads, understanding meiosis, explaining genetic diversity, comparing mitosis and meiosis, and explaining sperm and ova structural differences.

• The male gonads are the testes, and the female gonads are the ovaries.

• Both testes and ovaries produce gametes (sperm and ova or egg cells) that have half the genetic information of the parent.

Review of General Hypothalamic and Anterior Pituitary Control

• Gonadotropin-releasing hormone (GnRH) and other hormones control releases of FSH and LH in the testes and ovaries, and regulate the production and secretion of reproductive hormones and gametes.

Meiosis

• Meiosis is a type of nuclear division that produces gametes.

• Key differences between mitosis and meiosis include: meiosis produces four haploid cells, whereas mitosis produces two identical diploid cells; meiosis involves crossing over (exchange of genetic material between homologous chromosomes), which doesn't occur in mitosis.

Chromosomes

• Humans have 46 chromosomes (23 pairs), with 2 of the pairs being sex chromosomes.

• Autosomes are the 22 pairs of chromosomes that aren't sex chromosomes.

Meiosis in Females

• Meiosis I occurs before ovulation, creating a primary oocyte that is arrested in prophase I until fertilization, then it becomes a secondary oocyte.

• Meiosis II is completed if sperm fertilizes the secondary oocyte, otherwise it is released.

Sperm Cell

• Sperm cells have a head, midpiece, and tail. The head contains the nucleus and acrosome for digesting barriers. The midpiece has mitochondria, for energy ATP generation. The tail is for movement.

This quiz covers the key components and functions of the urinary system, as outlined in Fox Chapter 17. It includes details about the nephron's filtrate pathway and the kidneys' role in excretion and regulation. Test your understanding of the anatomy and physiology involved in urine production and transport.