Main Difference – Bladder vs Kidney
Bladder and kidney are two vital organs in the urinary system of animals. Bladder is a hollow, muscular organ that occurs in the pelvic floor. Kidneys are bean-shaped organs located below the rib cage on either side of the spine. The main difference between bladder and kidney is that bladder collects the urine from the kidney and stores it prior to the disposal through urination whereas kidney removes waste products and excess fluid from the body. The bladder resembles a pear in both size and shape when empty. Two ureters bring urine from each kidney to the bladder. Urethra is the duct that passes urine from the bladder to the outside of the body. Kidney regulates the salt, potassium, and acid content of the body. It also serves as an endocrine organ by producing hormones.
Key Areas Covered
1. What is Bladder
– Definition, Anatomy, Physiology
2. What is Kidney
– Definition, Anatomy, Physiology
3. What are the Similarities Between Bladder and Kidney
– Outline of Common Features
4. What is the Difference Between Bladder and Kidney
– Comparison of Key Differences
Key Terms: Bladder, Excretion, Kidney, Nephron, Osmolality Regulation, Renal Medulla, Transitional Epithelium, Urination, Urine
What is Bladder
Bladder is a muscular membranous sac, which receives urine from the kidney and stores it until urination. The ureter brings urine from the kidney to the bladder. The urine passes to the outside of the body through urethra in a process called urination. The volume of the urinary bladder depends on the amount of urine present in it. Urinary bladder is located in the pelvic cavity, superior to the reproductive structures and anterior to the rectum. It shares a limited space with the uterus in the pelvic cavity in females. The inner surface of the bladder consists of tiny wrinkles called rugae when empty. Two ureters are connected to the inferior and posterior walls of the bladder. The urethra starts at the inferior end of the bladder. The structure of the bladder is shown in figure 1.
Figure 1: Bladder
A mucosal layer produces the innermost layer of the bladder. Transitional epithelium lines the cavity of the bladder. The mucosal layer is surrounded by a submucosal tissue layer. The blood vessels and nervous tissue occur in the submucosal layer. Visceral muscles surround the submucosal layer. These muscles contract during the urination.
What is Kidney
Kidney is an organ pair in the abdominal cavity, which excretes urine. It is found in animals such as mammals, birds, and reptiles. Two kidneys are situated along the posterior muscular wall of the abdominal cavity behind the peritoneum. Three anatomical zones can be identified in a Kidney: renal capsule, renal cortex, and renal medulla. Renal medulla is composed of around seven renal pyramids; their bases face towards the renal cortex, and the apexes face towards the center of the kidney. Each apex connects to a minor calyx. Each calyx opens to the renal pelvis. The anatomy of the kidney is shown in figure 2.
Figure 2: Kidney Anatomy
The functional unit of the kidney is the nephron. It is responsible for the filtering of blood. A single kidney may contain about 1 million nephrons. The renal corpuscle and the renal tubule are the two components of a nephron. A renal corpuscle is made up of the Bowman’s capsule and the capillaries of the glomerulus. The Bowman’s capsule is made up of a special type of epithelial cells called podocytes. Proximal convoluted tubule, loop of Henle, distal convoluted tubule, and the collecting duct are the capillaries of a nephron. The anatomy of a nephron is shown in figure 3.
Figure 3: A Nephron
The three functions of the nephron are the filtration, reabsorption, and secretion. The final product of a nephron is called urine, which contains urea. Water homeostasis, acid/base homeostasis, electrolyte homeostasis, and blood pressure homeostasis are the major regulatory functions of the kidney. Calcitriol and erythropoietin are the two hormones produced by the kidney. Calcitriol increases the absorption of calcium in the intestinal tubule. Erythropoietin stimulates the bone marrow to produce red blood cells.
Similarities Between Bladder and Kidney
- Both bladder and kidney are organs in the urinary system.
- Both kidney and bladder are located in the abdominal cavity.
- Both bladder and kidney are involved in the excretion of waste materials from the body.
Difference Between Bladder and Kidney
Definition
Bladder: Bladder is a muscular membranous sac that receives urine from the kidney and stores it until urination.
Kidney: Kidney is an organ in the abdominal cavity, which excretes urine.
Location
Bladder: Bladder is located in the pelvic cavity, superior to the reproductive structures and anterior to the rectum.
Kidney: Two kidneys are situated along the posterior muscular wall of the abdominal cavity behind the peritoneum.
Peritoneum
Bladder: Bladder is located inferior to the peritoneum.
Kidney: Kidney is located behind the peritoneum.
Significance
Bladder: Bladder serves as the urine storage tank of the body.
Kidney: Kidney serves as the main excretory organ of the body.
Number
Bladder: There is only one bladder in the body.
Kidney: There are two kidneys in the body.
Shape
Bladder: Bladder is a spherical-shaped, hollow, muscular organ.
Kidney: Kidney is a bean-shaped organ.
Zones
Bladder: The wall of the bladder is composed of a transitional epithelial layer, submucosal layer, and a muscular tissue layer.
Kidney: Renal capsule, renal cortex, and renal medulla are the three zones of a kidney.
Function
Bladder: The major function of the bladder is to collect urine from the kidney and store until urination.
Kidney: The major functions of the kidney are the excretion of metabolic wastes from the body and regulation of the osmolality.
Conclusion
Bladder and kidney are two organs in the urinary system of animals. Bladder is a hollow, muscular organ, collecting and storing urine from kidneys until urination. There are two kidneys in the body. They filter blood to excrete metabolic wastes and excess water from the body. Therefore, the main difference between bladder and kidney is the function of each organ in the urinary system.
Reference:
1. “Urinary Bladder – Anatomy and Physiology.” Innerbody, Available here.
2. “Your Kidneys and How They Work.” National Institute of Diabetes and Digestive and Kidney Diseases, U.S. Department of Health and Human Services, 1 Mar. 2014, Available here.
Image Courtesy:
1. “2605 The Bladder” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “Blausen 0592 KidneyAnatomy 01” By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia
3. “Nephron Anatomy” By BruceBlaus – Own work (CC BY-SA 4.0) via Commons Wikimedia
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