Urinary and Reproductive Systems: Study Guide for Exam 4

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Chapter 25: The Urinary System

Anatomy and Functions of the Human Urinary System

The urinary system is responsible for removing waste products from the blood, regulating blood volume and pressure, controlling levels of electrolytes and metabolites, and regulating blood pH.

Main organs: Kidneys, ureters, urinary bladder, and urethra.
Primary functions: Filtration of blood, formation of urine, and excretion of metabolic wastes.
Homeostatic roles: Regulation of water, ion balance, and acid-base balance.

Anatomical Structure of the Kidneys

The kidneys are bean-shaped organs located retroperitoneally. Each kidney contains an outer cortex and an inner medulla, which is divided into renal pyramids. The functional unit of the kidney is the nephron.

Renal cortex: Outer region containing glomeruli and convoluted tubules.
Renal medulla: Inner region with renal pyramids and collecting ducts.
Renal pelvis: Funnel-shaped structure that collects urine and channels it to the ureter.

Kidney Function: Glomerulus, Nephrons, and Blood Vessels

The nephron consists of the renal corpuscle (glomerulus and Bowman’s capsule) and renal tubule (proximal tubule, loop of Henle, distal tubule, and collecting duct).

Glomerulus: Capillary network where filtration of blood occurs.
Bowman’s capsule: Surrounds the glomerulus and collects filtrate.
Peritubular capillaries: Surround the tubules and are involved in reabsorption and secretion.

Glomerular Filtration Rate (GFR) and Influencing Pressures

GFR is the volume of filtrate formed per minute by both kidneys. It is influenced by three main pressures:

Glomerular hydrostatic pressure (GHP): Promotes filtration.
Capsular hydrostatic pressure (CHP): Opposes filtration.
Blood colloid osmotic pressure (BCOP): Opposes filtration due to plasma proteins.

Equation:

Calculation of Solute Amounts

The amount of a solute filtered, reabsorbed, secreted, and excreted can be calculated as follows:

Filtered: Amount entering the nephron via filtration.
Reabsorbed: Amount returned to the blood from the tubule.
Secreted: Amount added to the tubule from the blood.
Excreted: Amount eliminated in urine.

Equation:

Source of Filtrate

Filtrate is derived from plasma that passes through the filtration membrane of the glomerulus into Bowman’s capsule.

Regulation of Glomerular Filtration Rate

GFR is regulated by intrinsic (renal autoregulation) and extrinsic (neural and hormonal) mechanisms:

Myogenic mechanism: Smooth muscle response to pressure changes.
Tubuloglomerular feedback: Macula densa cells sense NaCl concentration.
Hormonal control: Renin-angiotensin-aldosterone system (RAAS).

Fluid Excretion Efficiency

Despite high renal blood flow, only about 1% of filtered fluid is excreted as urine due to extensive reabsorption in the nephron.

Filtration Barriers

Three barriers separate the blood in glomerular capillaries from the lumen of Bowman’s capsule:

Fenestrated endothelium of glomerular capillaries
Basement membrane
Podocyte filtration slits

Major Renal Processes and Their Locations

Filtration: Occurs in the glomerulus.
Reabsorption: Occurs mainly in the proximal tubule, loop of Henle, distal tubule, and collecting duct.
Secretion: Occurs in the proximal and distal tubules and collecting duct.

Substances Secreted into Tubules

Substances such as H+, K+, NH4+, creatinine, and certain drugs are secreted into the renal tubules.

Reabsorption of Water and Solutes

Water and solutes are reabsorbed from the renal tubules into the peritubular capillaries by active and passive transport mechanisms, including osmosis and facilitated diffusion.

Regulation of Urine Volume

Urine volume is regulated by antidiuretic hormone (ADH), aldosterone, and the concentration gradient in the renal medulla.

Renin-Angiotensin-Aldosterone System (RAAS)

The RAAS regulates blood pressure and fluid balance. The kidneys release renin, which leads to the production of angiotensin II and stimulates aldosterone secretion from the adrenal cortex.

Organs involved: Kidneys, liver, lungs, adrenal glands.

Chapter 27: The Reproductive System

Structure and Function of the Testes

The testes are the male gonads responsible for producing sperm and testosterone. Each testis contains seminiferous tubules where spermatogenesis occurs.

Histology of Seminiferous Tubules: Sertoli and Leydig Cells

Sertoli cells: Support and nourish developing sperm cells; form the blood-testis barrier.
Leydig cells: Located in the interstitial tissue; produce testosterone.

Events of Spermatogenesis

Spermatogenesis is the process of sperm cell development, occurring in the seminiferous tubules:

Spermatogonia (stem cells) divide by mitosis.
Primary spermatocytes undergo meiosis I to form secondary spermatocytes.
Secondary spermatocytes undergo meiosis II to form spermatids.
Spermatids mature into spermatozoa (sperm cells).

Hormonal Regulation of Testicular Function

Gonadotropin-releasing hormone (GnRH): From hypothalamus; stimulates FSH and LH release from anterior pituitary.
FSH: Stimulates Sertoli cells and spermatogenesis.
LH: Stimulates Leydig cells to produce testosterone.

Ovaries: Location, Structure, and Function

The ovaries are the female gonads, located in the pelvic cavity. They produce oocytes (eggs) and secrete estrogen and progesterone.

Oogenesis vs. Spermatogenesis

Feature	Oogenesis	Spermatogenesis
Location	Ovaries	Testes
Timing	Begins before birth, completes after puberty	Begins at puberty, continues throughout life
Number of gametes	1 mature ovum per cycle	Millions of sperm daily
Cytokinesis	Unequal (polar bodies)	Equal

Stages of Follicle Development

Primordial follicle
Primary follicle
Secondary follicle
Vesicular (Graafian) follicle
Ovulation releases the oocyte

Ovarian Cycle Phases and Oogenesis Events

Follicular phase: Follicle growth and oocyte maturation.
Ovulation: Release of mature oocyte.
Luteal phase: Corpus luteum formation and hormone secretion.

Menstrual Cycle Phases

Menstrual phase: Shedding of endometrial lining.
Proliferative phase: Regeneration of endometrium.
Secretory phase: Preparation for implantation; endometrium thickens.

Hormonal Regulation of Ovarian and Menstrual Cycles

GnRH stimulates FSH and LH release.
FSH promotes follicle development.
LH triggers ovulation and corpus luteum formation.
Estrogen and progesterone regulate endometrial changes.

Physiological Effects of Estrogens and Progesterone

Estrogens: Promote development of female secondary sex characteristics, endometrial growth, and bone health.
Progesterone: Prepares endometrium for implantation, maintains pregnancy.

Fertilization

Fertilization is the process by which a sperm cell fuses with an oocyte to form a zygote, typically occurring in the fallopian tube. The sperm must penetrate the corona radiata and zona pellucida surrounding the oocyte.