THE EXCRETORY SYSTEM

EDILBERTO A. RAYNES, MD, PhD (Candidate)

ORGANS OF EXCRETION

ORGAN SUBSTANCE EXCRETED

KIDNEY WATER,ELECTROLYTES,NITROGENOUS WASTE,DRUGS

SKIN (SWEAT GLANDS) WATER,ELECTROLYTES, NITROGENOUS WASTE

ORGANS OF EXCRETION

ORGAN SUBSTANCE EXCRETED

LUNGS CARBON DIOXIDEWATER

INTESTINES DIGESTIVE WASTE (FECES)BILE PIGMENTS

FUNCTIONS OF URINARY SYSTEM

• ELIMINATE METABOLIC WASTES• REGULATE BLOOD pH AND ITS CHEMICAL

COMPOUND• REGULATE BLOOD VOLUME AND FLUID

BALANCE

FUNCTIONS OF URINARY SYTEM-CONT’D

• REGULATE BLOOD PRESSURE

• PLAY A ROLE IN THE REGULATION OF RED BLOOD CELL PRODUCTION

ELIMINATE METABOLIC WASTE

• EXCRETE NITROGENOUS WASTE SUCH AS UREA, AMMONIA AND CREATININE

• EXCRETE EXCESS POTASSIUM IONS, CARBON DIOXIDE, AND HEAT

REGULATE BLOOD pH AND ITS CHEMICAL COMPOUND

• BY CONTROLLING THE EXCRETION OF HYDROGEN IONS

REGULATE BLOOD VOLUME AND FLUID BALANCE

• BY DETERMINING THE AMOUNT OF WATER EXCRETED AND REABSORBED INTO THE CIRCULATORY SYSTEM

• EDEMA

REGULATE BLOOD PRESSURE

• BY SECRETING ENZYME, RENIN, THAT STIMULATE VASOCONSTRICTION

• BLOOD PRESSURE IS MAINTAINED BY INTERACTION OF CIRCULATORY, ENDOCRINE AND NERVOUS SYSTEM

ROLE IN RED BLOOD CELL PRODUCTION

• THROUGH THE SECRETION OF A HORMONE CALLED ERYTHROPOIETIN

ORGANS OF URINARY SYTEM AND INTERNAL STRUCTURE OF A KIDNEY

STRUCTURE OF A KIDNEY

• 3 DISTINCT REGIONS:1. RENAL CORTEX: OUTER CORTEX2. RENAL MEDULLA: LOCATED DEEP WITHIN

KIDNEY3. RENAL PELVIS:COLLECTS THE URINE MADE

BY THE KIDNEY AND HELPS FORM THE UPPER END OF URETER

RENAL CORTEX

• NEPHRONS: BASIC FILTERING UNITS OF THE KIDNEY THAT ARE RESPONSIBLE FOR FILTERING WASTE PRODUCTS FROM THE BLOOD

URINE MAKING: THE NEPHRON UNIT

• NEPHRON: FUNCTIONAL UNIT (1 M PER KIDNEY)

• 2 PARTS: 1. RENAL BLOOD TUBULES2. RENAL BLOOD VESSELS

URINE FORMATION OCCURS IN SEQUENCE OF TUBULAR STRUCTURES

• BOWMAN’S CAPSULE• PROXIMAL CONVOLUTED TUBULE (PCT)• DESCENDING LIMB OF HENLE• ASCENDING LIMB OF HENLE• DISTAL CONVOLUTED TUBULE (DCT)• COLLECTING DUCT• CALYX• RENAL PELVIS

RENAL BLOOD VESSELS

RENAL ARTERY AFFERENT ARTERIOLE EFFERENT ARTERIOLE THEN FORMS A SECOND CAPILLARY NETWORK CALLED THE PERITUBULAR CAPILLARIES EMPTY INTO THE VENULES, LARGER VEINS, AND INTO THE RENAL VEIN.

SEQUENCE OF VASCULAR STRUCTURES

RENAL ARTERY

SMALLER AND SMALLER ARTERIES

AFFERENT ARTERIOLE

SEQUENCE OF VASCULAR STRUCTURES

GLOMERULUS

EFFERENT ARTERIOLE

PERITUBULAR CAPILLARY

SEQUENCE OF VASCULAR STRUCTURES

RENAL VENULES

LARGER VEINS

RENAL VEIN

INFERIOR VENA CAVA

URINE FORMATION• URINE IS FORMED IN THE NEPHRON UNITS AS

WATER AND DISSOLVED SUBSTANCES MOVE BETWEEN THE VASCULAR STRUCTURES AND TUBULAR STRUCTURES.

• THREE PROCESSES: 1. GLOMERULAR FILTRATION2. TUBULAR REABSORPTION3. TUBULAR SECRETION

GLOMERULAR FILTRATION

• THE FORMATION OF URINE BEGINS IN THE GLOMERULUS AND BOWMAN’S CAPSULE

• GLOMERULAR FILTRATION CAUSES WATER AND DISSOLVED SUBSTANCES TO MOVE FROM GLOMERULUS INTO BOWMAN’S CAPSULE.

WHY FILTRATION OCCURS?

• FILTRATION OCCURS WHEN THE PRESSURE ON ONE SIDE OF A MEMBRANE IS GREATER THAN THE PRESSURE ON THE OPPOSITE SIDE.

• BLOOD PRESSURE IN THE GLOMERULUS IS HIGHER THAN THE PRESSURE WITHIN BOWMAN’S CAPSULE THEREBY PROVIDING THE DRIVING FORCE FOR FILTRATION.

WHAT SUBSTANCES ARE FILTERED?

• WATER, SODIUM, POTASSIUM, CHLORIDE, GLUCOSE, URIC ACID, AND CREATININE MOVE THROUGH THE PORES VERY EASILY. THESE SUBSTANCES ARE FILTERED IN PROPORTION TO THEIR PLASMA CONCENTRATION.

• LARGE MOLECULES: RED BLOOD CELLS AND LARGE PROTEINS REMAIN WITHIN THE GLOMERULUS.

WHAT SUBSTANCES ARE FILTERED?GLOMERULAR FILTRATE• WATER AND DISSOLVED SUBSTANCES• PROTEIN-FREEGLOMERULAR FILATRATION RATE (GFR): RATE AT

WHICH GLOMERULAR FILTRATION OCCURS.; 125 ML PER MINUTE OR 180 LITERS (45 GALLONS) PER DAY

A PERSONEXCRETES ONLY 1.5 L/DAY; 178.5 L ARE FILTERED BUT NOT EXCRETED

TUBULAR REABSORPTION

• THE PROCESS BY WHICH WATER AND DISSOLVED SUBSTANCES (GLOMERULAR FILTRATE) MOVE FROM THE TUBULES INTO THE BLOOD OF THE PERITUBULAR CAPILLARIES.

• ALTHOUGH OCCURS THROUGHOUT THE ENTIRE LENGTH OF THE RENAL TUBULE BUT MOST OCCURS IN THE PROXIMAL CONVOLUTED TUBULE.

WHAT IS REABSORBED AND WHAT IS EXCRETED?

• THE KIDNEY SELECTS THE TYPE AND QUANTITY OF SUBSTANCES IT REABSORBS.

• SOME SUBSTANCES, LIKE GLUCOSE, ARE COMPLETELY REABSORBED. AMOUNT OF GLUCOSE FILTERED=AMOUNT REABSORBED THEREFORE NO GLUCOSE APPEARS IN URINE

WHAT IS REABSORBED AND WHAT IS EXCRETED?

• SOME SUBSTANCES ARE INCOMPLETELY REABSORBED. OVER 99% OF WATER AND SODIUM IS REABSORBED WHILE ONLY 50% OF UREA IS REABSORBED.

• SOME WASTE PRODUCTS SUCH SUCH AS CREATININE ARE NOT REABSORBED AND REMAIN IN THE TUBULES BECOMING A PART OF THET URINE.

MECHANISM OF REABSORPTION

• ABSORPTION OCCURS THROUGH EITHER ACTIVE OR PASSIVE TRANSPORT.

• SODIUM IS ACTIVELY TRANSPORTED FROM THE TUBULES INTO THE PERITUBULAR CAPILLARIES.

• WATER AND CHLORIDE PASSIVELY FOLLOW THE MOVEMENT OF SODIUM.

MECHANISM OF REABSORPTION-DIURETICS

• WHEN SODIUM IS PUMPED FROM ONE LOCATION TO ANOTHER, WATER FOLLOWS PASSIVELY. THIS FORMS THE BASIS OF THE ACTION OF DIURETICS, A DRUG THAT INCREASES THE URINE PRODUCTION.

• MOST DIURETICS BLOCK THE TUBULAR REABSORPTION OF WATER. THE EXCESS SODIUM AND WATER IN THE TUBULES ARE ELIMINATED AS URINE.

TUBULAR SECRETION

• INVOLVES THE ACTIVE SECRETION OF POTASSIUM (K+); HYDROGEN IONS (H+); URIC ACID; AMMONIUM IONS; AND DRUGS FROM THE PERITUBULAR CAPILLARIES INTO THE TUBULES.

IN A NUTSHELL: URINE FORMATION

• FILTRATION: CAUSES WATER AND DISSOLVED SUBSTANCES TO MOVE FROM THE CAPILLARIES (GLOMERULUS) INTO THE TUBULES

• REABSORPTION: CAUSES WATER AND SELECTED SUBSTANCES TO MOVE FROM THE TUBULES INTO THE PERITUBULAR CAPILLARIES

• SECRETION: CAUSES SMALL AMOUNTS OF SPECIFIC SUBSTANCES TO MOVE FROM THE PERITUBULAR CAPILLARIES INTO THE TUBULES