The Urinary System and Tract A continued examination

Figure 26.10 Glomerular Filtration Figure 26.10a, b

Glomerular filtration rate (GFR) Amount of filtrate produced in the kidneys each minute Factors that alter filtration pressure change GFR

Factors controlling the GFR A drop in filtration pressure can activate local mechanisms--results in vasodilation of afferent arterioles and vasoconstriction of efferent arterioles----> increase in glomerular (filtration) pressure A drop in filtration pressure stimulates Juxtaglomerular apparatus (JGA) Releases renin and erythropoietin

Figure 26.11 The Response to a Reduction in the GFR Figure 26.11a

Figure 26.11 The Response to a Reduction in the GFR Figure 26.11b

Sympathetic activation Produces powerful vasoconstriction of afferent arterioles Decreases GFR and slows production of filtrate Usually in response to big drop in blood pressure Changes the regional pattern of blood flow Alters GFR

Reabsorption and secretion at the DCT DCT performs final adjustment of urine Active secretion or absorption Absorption Tubular cells actively resorb Na+ and Cl- In exchange for potassium or hydrogen ions (secreted)

Figure 26.14 Tubular Secretion and Solute Reabsorption at the DCT PLAY Animation: Distal Convoluted Tubule Figure 26.14

Figure 26.14 Tubular Secretion and Solute Reabsorption at the DCT Figure 26.14c

Reabsorption and secretion along the collecting system Water and solute loss is regulated by aldosterone and ADH Reabsorption Sodium ion, bicarbonate, and urea are resorbed Secretion pH is controlled by secretion of hydrogen or bicarbonate ions

Control of urine volume and osmotic concentration Urine volume and osmotic concentration are regulated by controlling water reabsorption Precise control allowed via facultative water reabsorption

Figure 26.15 The Effects of ADH on the DCT and Collecting Ducts

Figure 26.15 The Effects of ADH on the DCT and Collecting Ducts Figure 26.15a, b

Function of the vasa recta Removes solutes and water Balances solute reabsorption and osmosis in the medulla

Composition of normal urine Varies with the metabolic and hormonal events of the body Reflects filtration, absorption and secretion activity of the nephrons Urinalysis is the chemical and physical analysis of urine

Summary of renal function: Each segment of nephron and collecting system contribute Glomerulus PCT Descending limb Thick ascending limb DCT and collecting ducts Concentrated urine produced after considerable modification of filtrate PLAY Animation: Late Filtrate Processing

Figure 26.16 A Summary of Renal Function

Figure 26.16 A Summary of Renal Function Figure 26.16b

Chapter 26, part 4 The Urinary System

SECTION 26-6 Urine Transport, Storage, and Elimination

Urine production ends with fluid entering the renal pelvis Rest of urinary system transports, stores and eliminates Ureters Bladder Urethra

Figure 26.17 A Radiographic View of the Urinary System

The ureters Pair of muscular tubes Extend from renal pelvis to the bladder Peristaltic contractions force urine toward the urinary bladder

The urinary bladder Hollow, muscular organ Internal features include Reservoir for the storage of urine Contraction of detrusor muscle voids bladder Internal features include Trigone Neck Internal urethral sphincter Ruggae

Figure 26.19 Organs for the Collection and storage of Urine Figure 26.19a

Figure 26.19 Organs for the Collection and storage of Urine Figure 26.19b

Figure 26.19 Organs for the Collection and storage of Urine Figure 26.19c

The urethra Extends from the urinary bladder to the exterior of the body Passes through urogenital diaphragm (external urinary sphincter) Differs in length and function in males and females

Figure 26.20 The Histology of the Organs that Collect and Transport Urine Figure 26.20a

Figure 26.20 The Histology of the Organs that Collect and Transport Urine Figure 26.20b, c

Micturition reflex and urination Urination coordinated by micturition reflex Initiated by stretch receptors in wall of bladder Urination requires coupling micturition reflex with relaxation of external urethral sphincter

Figure 26.21 The Micturition Reflex

Figure 26.21 The Micturition Reflex

SECTION 26-7 Aging and the Urinary System

Changes with aging include: Decline in the number of functional nephrons Reduction of GFR Reduced sensitivity to ADH Problems with the micturition reflex

You should now be familiar with: The components of the urinary system and their functions The location and structural features of the kidneys The structure of a nephron, and the processes involved in the formation of urine The normal characteristics, composition, and solute concentrations of a representative urine sample

You should now be familiar with: The factors that influence filtration pressure and the rate of filtrate formation The types of transport mechanisms found along the nephron How antidiuretic hormone and aldosterone levels influence the volume and concentration of urine