BSC2086 Final Exam Review: Chapters 25-28
Renal Anatomy and the Urinary System
The kidneys are located in a position known as retroperitoneal, meaning they are situated behind the peritoneum within the abdominal cavity. Anatomically, the kidney is divided into distinct regions; the outer region is called the cortex. The functional unit of the kidney, responsible for filtration and urine formation, is the nephron. Most nephrons in the human body, approximately , are classified as cortical nephrons, while the remaining are juxtamedullary nephrons. A significant anatomical feature of the nephron is the loop of Henle; a longer loop of Henle is specifically adapted to concentrate urine more effectively.
Urine follows a specific pathway for excretion. It is formed in the nephrons and eventually empties from the collecting ducts into the minor calyx, then into the major calyx, and finally into the renal pelvis. From the renal pelvis, urine leaves the kidney via the ureters. The ureters move urine toward the bladder using peristalsis. The urinary bladder is lined with a specialized type of epithelium known as transitional epithelium, which allows for stretching. The primary muscle of the bladder wall is the detrusor muscle. Urine is finally expelled through the urethra. In males, the urethra is divided into three distinct segments: the prostatic urethra, the membranous urethra, and the spongy urethra.
Renal Physiology and Filtration
In the renal corpuscle, the afferent arteriole leads directly into the glomerulus, which consists of a network of fenestrated capillaries. This fenestration allows for the filtration of blood. The glomerulus is encapsulated by a structure known as Bowman's capsule. The filtration rate is critical for health; if the Glomerular Filtration Rate (GFR) decreases significantly, it leads to waste accumulation in the blood. The juxtaglomerular cells are responsible for secreting Renin, an enzyme involved in blood pressure and elective regulation.
The nephron segments handle water and solutes differently. The majority of all reabsorption occurs in the proximal convoluted tubule (PCT). Regarding the loop of Henle, the descending loop is permeable to water, whereas the ascending loop is impermeable to water because it is specialized for the transport of certain ions. Hormonal regulation further dictates tubule function. Aldosterone acts primarily on the distal convoluted tubule (DCT) to regulate sodium and potassium. ADH (antidiuretic hormone or vasopressin) acts most significantly on the collecting duct to regulate water reabsorption.
Fluid, Electrolytes, and Acid-Base Balance
Electrolyte balance is vital for physiological function. Hyponatremia is a clinical condition caused by low sodium levels in the blood. Conversely, high potassium blood levels are dangerous as they can lead to arrhythmia. To manage sodium levels, the body utilizes Atrial Natriuretic Peptide (ANP), which works to increase sodium excretion.
The body regulates pH through multiple systems. The fastest acting buffer system is the bicarbonate buffer system. The respiratory system regulates pH through the removal of . The kidneys regulate pH by excreting hydrogen ions () and performing bicarbonate () reabsorption. The normal pH range for urine is between and .
Male Reproductive System
The male gonads are the testes, which serve two primary functions: the production of gametes, known as spermatozoa, and the production of testosterone. Sperm are specifically formed within the seminiferous tubules and then move to the epididymis where they undergo maturation. Testosterone is produced by the Leydig cells, also known as interstitial cells. This hormone is responsible for several key functions: the development of secondary male characteristics, the maturation of sperm, and the increase of muscle mass and metabolism.
Seminal fluid is produced by three accessory glands. The seminal vesicles produce of the bulk of semen; this fluid is high in fructose and is alkaline. The prostatic gland adds fluid to the semen and helps with the process of ejaculation. The bulbourethral gland produces pre-ejaculate, which serves to alkalinize the urethra. During ejaculation, sperm travels through the ductus deferens (or vas deferens) to the ejaculatory duct, where it joins the prostatic urethra. The ductus deferens is connected to the testicles via the spermatic cord, which contains vasculature and a network of nerves known as the pampiniform plexus.
Female Reproductive System and Cycles
The female gonads are the ovaries, which produce gametes called oocytes. The uterus is composed of three layers: the endometrium (inner), the myometrium (middle muscle layer), and the perimetrium (outer). Anatomically, the uterus is divided into the fundus, the body, and the cervix. Estrogen causes the thickening of the endometrium in preparation for potential pregnancy. The fallopian tubes (or uterine tubes) consist of several sections: the fimbriae, the infundibulum, the ampulla, and the isthmus. Fertilization typically occurs within the fallopian tube.
The female reproductive cycle is regulated by hormones from the anterior pituitary. Luteinizing hormone (LH) triggers ovulation, while Follicle Stimulating Hormone (FSH) stimulates follicle growth in females (and spermatogenesis in males). Following ovulation, the ovary enters the luteal phase, and the uterus enters the secretory phase, which is led by progesterone. Progesterone is produced on a monthly basis by the corpus luteum.
Embryology and Human Development
Fertilization occurs when a sperm uses digestive enzymes stored in its acrosome to penetrate the corona radiata and zona pellucida of the oocyte. The immediate product of fertilization is a single-celled zygote. This zygote undergoes cleavage; a solid ball of cells is called a morula. Implantation into the uterine wall occurs at the blastocyst stage. The placenta is derived from a tissue called the trophoblast. Specifically, the syncitiotrophoblast produces human chorionic gonadotropin (hCG), which is the hormone detected by pregnancy tests. hCG signals the body to maintain the corpus luteum, thereby maintaining progesterone levels.
Further development involves gastrulation, which is the process of differentiation into a trilaminar disc consisting of three germ layers. The ectoderm is the layer that develops into the nervous system and the skin. Organogenesis, the formation of organs, occurs mostly during the first trimester of pregnancy. Childbirth is medically referred to as parturition. Hormonal control of late pregnancy and nursing includes oxytocin, which stimulates uterine contractions and the milk let-down reflex, and prolactin, which stimulates milk production.
Genetics and Heredity
Genetics is the study of DNA and inheritance. The female genotype is defined as . A dominant trait or allele only requires one allele to be expressed in the phenotype. A heterozygous genotype is represented as . The SRY gene is specifically responsible for male development. Genetic outcomes and probabilities can be predicted using a tool called a Punnett square. A mutation is defined as a change in the DNA sequence. In the case of twins, identical twins are referred to as monozygotic.