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…

A.Y. is a 33-year-old woman with a history of severe asthma requiring multiple admissions and intubations, who initially presented to the emergency room with shortness of breath, wheezing, and chest pain. Presentation: History A.Y. had been in her usual state of health until this morning, when she had a sudden sensation of “tightness” in her chest accompanied by wheezing and shortness of breath. She cannot name…

Core concepts ( figs. 16.1 and 16.2 ) To function properly, the human respiratory system must: Respond to oxygen demands. Maintain a constant range of oxygen and carbon dioxide in blood. Respiration is governed by both voluntary and involuntary neural pathways. Voluntary control allows talking, eating, and drinking. Involuntary control allows respiration through wakefulness and periods of unconsciousness (i.e., sleep). Neural pathways mediating respiration are sensitive…

Introduction For successful cell respiration to occur, multiple systems must work in unison for the transport of oxygen (O 2 ) and carbon dioxide (CO 2 ): Respiratory system Hematologic system Cardiovascular system Both O 2 and CO 2 traverse these systems (blood, alveoli, and tissues) via simple diffusion. O 2 : air → alveoli → pulmonary capillaries → systemic circulation → tissue CO 2 :…

Introduction Why do we breathe? The vital importance of breathing was clear even in ancient times, when people believed that the air we breathe, or pneumo , gives rise to the spirit. Oxygen in the air enables active cellular metabolism, enabling optimal function at the cellular level and ultimately proper functioning of all of the body’s organ systems. Ultimately, the lungs bear two important responsibilities: To…

Introduction The use of oxygen for energy extraction is called aerobic respiration. In humans, gas exchange occurs in the air-filled lungs, which exposes the blood of the circulatory system to the air. Oxygen in the air of the lungs diffuses into the blood. Carbon dioxide brought from the body tissues diffuses out of the blood into the air in the lungs. For this exchange to occur…

L.B. is a 68-year-old retired accountant who has noticed worsening shortness of breath while mowing his lawn. Presentation: History L.B. was well until 6 months ago, when he noticed extreme fatigue and lightheadedness when moving from a sitting or lying to a standing position. Initially, he blamed this on lack of sleep because of shortness of breath in bed, relieved by propping his head on two…

Introduction Whether running a marathon or toting a hefty biochemistry book up a staircase, exercising muscle places demand on the body through three mechanisms: Increased oxygen and nutrient demand Increased waste products of metabolism Increased heat generation The cardiovascular, respiratory, and temperature-regulating systems of the body must adapt to meet the demands of exercising muscles. System function For a discussion of system structure, please refer to…

Introduction The heart contains specialized tissue for: (1) generating rhythmic action potentials and (2) conducting those action potentials precisely across the heart. This ensures correct timing of atrial and ventricular contraction. System structure Fig. 11.1 depicts the typical pathway of cardiac excitation. Action potentials are transmitted from sinoatrial (SA) node to atrioventricular (AV) node. Excitation proceeds through atrial muscle and specialized conducting tissues: His bundle Bundle…

Introduction As mentioned in Chapter 9 , the heart is the muscular organ that serves as the pump driving the flow of blood through the cardiovascular system. System structure Located in the mediastinum of the chest at the level of thoracic vertebrae T5–T8, the human heart is a four-chambered pump surrounded by a fibrous sac ( Fig. 10.1 ). Pericardium Most superficial tissue of the heart.…

Introduction The cardiovascular system serves as the principal transportation and distribution network of the body, allowing: Delivery of several essential substances (e.g., glucose and oxygen) to the tissues Removal of by-products of metabolism (e.g., carbon dioxide, lactate, and heat) In its simplest formulation, the system is composed of three parts: 1. Pump (the heart) 2. Series of distributing and collecting tubes (the arterial and venous systems)…

Note: This case will be presented in a slightly different format, to facilitate our discussion of the sequence of the “normal” immune response. A.P. is a 69-year-old man with hypertension (well controlled, on medications), hypercholesterolemia, and osteoarthritis of the right knee who presents with a cough, sore throat, muscle aches, and low-grade fever (100° F). On history, he remarks that he visited his grandchildren a few…

Introduction The lymphatic system plays two essential roles in the human body: 1. Absorbs fluid from interstitial space and returns fluid to intra-vascular space. a. Transports lymph filtration fluid that enters the interstitial space from the capillaries. 2. Functional connection of blood and endothelium to the immune system. a. Transport of immune cells and products. Lymphatic system structure The lymphatic system plays an essential role in…

Introduction Blood is a specialized type of connective tissue that performs several key functions required for the viability of all other organs: Major transportation route via the circulatory system. Brings oxygen and nutrients (i.e., glucose), as well as endocrine hormones. Removes carbon dioxide and waste products for disposal. Maintains body temperature. Provides defense against infection. System structure The structure of blood differs in two important aspects…