Introduction The menstrual cycle defines the reproductive years of a woman’s life. It begins with menarche (the onset of menstruation) at about age 8 to 13 years and ends with menopause, which begins at about age 50 years. Evolutionarily, the purpose of each menstrual cycle is to create the opportunity for pregnancy. Preparation for potential pregnancy is achieved through two concurrent cycles, which together make up…

Introduction The word skeleton comes from the Greek skellein, meaning to dry up; a dried-up body (skeleton soma) is one with only the bones remaining. Thus etymologically, but also in our cultural imagination, our bones refer to death. However, the skeleton is, like any other organ system, a system dedicated entirely to the functions of life. The human skeleton is made not only of minerals, but…

Introduction Calcium plays a fundamental role in the physiology of all living organisms. At the macroscopic level, calcium is essential to maintaining the structural integrity of the skeleton. At the molecular level, calcium is central to several physiologic processes, including neurotransmitter release, signal transduction, and blood coagulation. Parathyroid hormone (PTH), the main product of the parathyroid glands, and vitamin D together regulate the serum calcium level.…

Introduction The adrenal gland plays a pivotal role in human endocrine physiology. It is subdivided into two sections, which function separately and originate from different embryonic tissues. The outermost shell of the adrenal gland, the adrenal cortex, is divided into three layers: 1. Zona glomerulosa 2. Zona fasciculata 3. Zona reticularis Together, these layers produce three kinds of steroid hormones: 1. Aldosterone, a mineralocorticoid, modulates electrolyte…

Introduction The thyroid—named from the Greek thureoeides , meaning “shield-shaped”—bears two essential responsibilities in the endocrine system: Maintains metabolic rate necessary for heat generation in warm-blooded species. Promotes normal growth and development from fetal life into childhood. Roughly 5% of the U.S. population has a diagnosed thyroid disorder, and perhaps another 5% has undiagnosed thyroid disease, according to the American Association of Clinical Endocrinologists. In developing…

Introduction The hypothalamus and pituitary gland constitute an elegant center of hormonal control known as the hypothalamic-pituitary axis (HPA). Each hormone controlled by the pituitary is regulated separately along its own pathway, or “axis.” The HPA integrates information from the body’s internal and external environments with higher cortical input. The HPA then orchestrates changes in the multiple physiologic systems controlled by the pituitary hormone axes, allowing…

Introduction In the 1920s, Frederick Banting and Charles Best isolated insulin and made possible the treatment and survival of millions of diabetics. This helped initiate the era of modern medicine, in which the empiricism of the 18th century and its practice in the 19th century came to fruition in the wondrous cures of the 20th century. This discovery was made possible by early research into pancreatic…

D.L. is a 9-year-old female who is being seen by her pediatrician for the fifth time this summer. She has been seen for multiple gastrointestinal (GI) complaints including abdominal pain, bloating, and frequent nausea. Her mother is worried because she continues to lose weight despite being given extra servings of food at meals and close monitoring. Presentation: History and physical examination D.L. has had multiple visits…

Introduction As described in Chapter 8 , the immune system is a complex cellular network that defends the body against danger. To do so, the immune system must distinguish between safe and dangerous substances. Safe or nonthreatening substances can be part of the body itself (e.g., normal extracellular molecules, cells, and tissues) or foreign (e.g., foods and commensal bacterial). Dangerous materials can be part of the…

Introduction The kidney modifies the contents of the plasma by filtering its components into the urine, whereas the liver modifies the blood contents by metabolically transforming them. The liver is where drugs, hormones, and toxic waste products, such as ammonia, are metabolized to inactive forms. The liver also plays an important role in carbohydrate metabolism. Specifically, the liver is involved in: Glycogen storage. Gluconeogenesis. Formation of…

Introduction In Chapter 24 , we saw that the acquisition of energy and building blocks requires digestion and absorption. We now focus on two other critical gastrointestinal (GI) capabilities, without which digestion and absorption could not occur: Motility is the muscular capacity for movement by which the digestive organs agitate food mechanically and propel it through the GI tract. Secretion is the process that delivers digestive…

Introduction The gastrointestinal (GI) system supplies the fuel and the building blocks for the functioning of the body through the digestion and absorption of nutrients. Its machinery for doing so is the alimentary canal, also called the gastrointestinal tract, a highly specialized long tube that connects the mouth and the anus. While providing for the absorption of essential nutrients and elimination of waste products, the GI…

C.J. is a 52-year-old male with chronic hypertension (HTN) managed both with lifestyle changes and pharmacologically. He presented yesterday morning to an outside hospital with malignant HTN, headache, and complaints of “tearing” chest pain. His only past medical history is labile HTN and borderline type 2 diabetes, he has never had surgery. Presentation: History and physical examination In the morning while walking to the bathroom, C.J.…

Introduction Micturition is the process by which the urinary bladder empties its contents, and it is more commonly known as urination. This process involves two steps: (1) the bladder fills until wall tension exceeds a certain threshold level and (2) a nervous reflex known as the micturition reflex occurs, and the bladder empties. The micturition reflex is an autonomic spinal cord reflex, occurring independently of signals…

Introduction Bodily processes are exquisitely sensitive to pH. Deviations from the normal range of blood pH of 7.35 to 7.45 may have serious consequences. Low pH (<7.2) causes significant clinical manifestations, including impaired growth, decreased cardiac output, decreased blood pressure, insulin resistance, and hyperkalemia. High pH (>7.6) is equally destructive, producing disturbances in heart rhythm and tetany from low free calcium. This pH sensitivity reflects the…

Introduction In the past few chapters, we made several observations about extracellular fluid (ECF) volume and osmolality: The stability of these parameters is critical for normal physiologic functioning These parameters are subject to daily changes The kidney counters these changes to preserve stable ECF volume and osmolality. In this chapter and the next, we will see that the same principles apply to two other critical physiologic…

Introduction Osmolality (or concentration of the solutes in the body fluids) is critical to organ function and must be closely regulated. Disturbances in the osmolality of the body fluids arise from the gain or loss of water, or from the gain or loss of osmoles (glucose, urea, salts). Accordingly, normal plasma osmolality is restored by: Excretion of extra water Replenishment of lost water Restoration of normal…

Introduction Organ perfusion, and therefore function, is dependent on blood pressure (BP). The cardiovascular system does not govern BP by itself; equally important to the regulation of BP is the kidney’s control over the volume of the extracellular fluid (ECF). Recall that systemic blood pressure (SBP) is equal to the product of cardiac output (CO) and systemic vascular resistance (SVR). SBP=CO×SVR SBP = CO × SVR…

Introduction The body faces multiple challenges met by the kidneys, including acid base balance, regulation of the concentrations of electrolytes such as potassium, and control of blood pressure. Two of the most critical are (1) the management of extracellular fluid volume by the handling of sodium and water and (2) the removal of metabolites and dietary components that are useful at low concentrations but toxic at…

Introduction The kidney is the principal organ of homeostasis. The kidney’s filtration of blood, and modification of that filtrate by epithelial transport, produces urine to accomplish the following functions: Control of the composition of body fluids, the concentration of electrolytes, and the excretion of metabolic waste products and foreign substances. Control of body fluid volume and osmolality. Regulation of the acidity of the blood. The kidney…